Answer:
The speed of the current is 3 miles per hour
Step-by-step explanation:
The equations for rate (r), distance (d), and time (t) are ⇒ d = rt, r = d/t, = t = d/r
Let x = speed in still water
Let c = speed of the current
The main difference with these problems is rate needs to be expressed using two variables because moving upstream the current is against you and downstream it moves with you.
Distance Rate Time
Upstream x − c
Downstream x + c
The distance column with the numbers from the problem and the value for speed in still water for x.
Distance Rate Time
Upstream 4 5 − c
Downstream 16 5 + c
The column for time using the other two columns knowing that rate, distance ⇒ time = Distance Rate Time
Upstream 4 5 − c
5 − c
4
Downstream 16 5 + c
5 + c
16
“It takes as long …” from the problem means that the two times are equal to each other. So, the equation can be written as:
4/5− c = 16/5 + c ⇒ Solve by cross-multiplying ⇒ 5(4 + c) = 16 5( − c) ⇒ c = 3
Differentiate both sides of the equation.<span><span><span>d<span>dx</span></span><span>(<span>x3</span>+<span>y3</span>)</span>=<span>d<span>dx</span></span><span>(18xy)</span></span><span><span>d<span>dx</span></span><span>(<span>x3</span>+<span>y3</span>)</span>=<span>d<span>dx</span></span><span>(18xy)</span></span></span>Differentiate the left side of the equation.Tap for fewer steps...By the Sum Rule, the derivative of <span><span><span>x3</span>+<span>y3</span></span><span><span>x3</span>+<span>y3</span></span></span> with respect to <span>xx</span> is <span><span><span>d<span>dx</span></span><span>[<span>x3</span>]</span>+<span>d<span>dx</span></span><span>[<span>y3</span>]</span></span><span><span>d<span>dx</span></span><span>[<span>x3</span>]</span>+<span>d<span>dx</span></span><span>[<span>y3</span>]</span></span></span>.<span><span><span>d<span>dx</span></span><span>[<span>x3</span>]</span>+<span>d<span>dx</span></span><span>[<span>y3</span>]</span></span><span><span>d<span>dx</span></span><span>[<span>x3</span>]</span>+<span>d<span>dx</span></span><span>[<span>y3</span>]</span></span></span>Differentiate using the Power Rule which states that <span><span><span>d<span>dx</span></span><span>[<span>xn</span>]</span></span><span><span>d<span>dx</span></span><span>[<span>xn</span>]</span></span></span> is <span><span>n<span>x<span>n−1</span></span></span><span>n<span>x<span>n-1</span></span></span></span> where <span><span>n=3</span><span>n=3</span></span>.<span><span>3<span>x2</span>+<span>d<span>dx</span></span><span>[<span>y3</span>]</span></span><span>3<span>x2</span>+<span>d<span>dx</span></span><span>[<span>y3</span>]</span></span></span>Evaluate <span><span><span>d<span>dx</span></span><span>[<span>y3</span>]</span></span><span><span>d<span>dx</span></span><span>[<span>y3</span>]</span></span></span>.Tap for more steps...<span><span>3<span>x2</span>+3<span>y2</span><span>d<span>dx</span></span><span>[y]</span></span><span>3<span>x2</span>+3<span>y2</span><span>d<span>dx</span></span><span>[y]</span></span></span>Differentiate the right side of the equation.Tap for fewer steps...Since <span>1818</span> is constant with respect to <span>xx</span>, the derivative of <span><span>18xy</span><span>18xy</span></span> with respect to <span>xx</span> is <span><span>18<span>d<span>dx</span></span><span>[xy]</span></span><span>18<span>d<span>dx</span></span><span>[xy]</span></span></span>.<span><span>18<span>d<span>dx</span></span><span>[xy]</span></span><span>18<span>d<span>dx</span></span><span>[xy]</span></span></span>Differentiate using the Product Rule which states that <span><span><span>d<span>dx</span></span><span>[f<span>(x)</span>g<span>(x)</span>]</span></span><span><span>d<span>dx</span></span><span>[f<span>(x)</span>g<span>(x)</span>]</span></span></span> is <span><span>f<span>(x)</span><span>d<span>dx</span></span><span>[g<span>(x)</span>]</span>+g<span>(x)</span><span>d<span>dx</span></span><span>[f<span>(x)</span>]</span></span><span>f<span>(x)</span><span>d<span>dx</span></span><span>[g<span>(x)</span>]</span>+g<span>(x)</span><span>d<span>dx</span></span><span>[f<span>(x)</span>]</span></span></span> where <span><span>f<span>(x)</span>=x</span><span>f<span>(x)</span>=x</span></span> and <span><span>g<span>(x)</span>=y</span><span>g<span>(x)</span>=y</span></span>.<span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y<span>d<span>dx</span></span><span>[x]</span>)</span></span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y<span>d<span>dx</span></span><span>[x]</span>)</span></span></span>Rewrite <span><span><span>d<span>dx</span></span><span>[y]</span></span><span><span>d<span>dx</span></span><span>[y]</span></span></span> as <span><span><span>d<span>dx</span></span><span>[y]</span></span><span><span>d<span>dx</span></span><span>[y]</span></span></span>.<span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y<span>d<span>dx</span></span><span>[x]</span>)</span></span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y<span>d<span>dx</span></span><span>[x]</span>)</span></span></span>Differentiate using the Power Rule which states that <span><span><span>d<span>dx</span></span><span>[<span>xn</span>]</span></span><span><span>d<span>dx</span></span><span>[<span>xn</span>]</span></span></span> is <span><span>n<span>x<span>n−1</span></span></span><span>n<span>x<span>n-1</span></span></span></span> where <span><span>n=1</span><span>n=1</span></span>.<span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y⋅1)</span></span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y⋅1)</span></span></span>Multiply <span>yy</span> by <span>11</span> to get <span>yy</span>.<span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y)</span></span><span>18<span>(x<span>d<span>dx</span></span><span>[y]</span>+y)</span></span></span>Simplify.Tap for more steps...<span><span>18x<span>d<span>dx</span></span><span>[y]</span>+18y</span><span>18x<span>d<span>dx</span></span><span>[y]</span>+18y</span></span>Reform the equation by setting the left side equal to the right side.<span><span>3<span>x2</span>+3<span>y2</span>y'=18xy'+18y</span><span>3<span>x2</span>+3<span>y2</span>y′=18xy′+18y</span></span>Since <span><span>18xy'</span><span>18xy′</span></span> contains the variable to solve for, move it to the left side of the equation by subtracting <span><span>18xy'</span><span>18xy′</span></span> from both sides.<span><span>3<span>x2</span>+3<span>y2</span>y'−18xy'=18y</span><span>3<span>x2</span>+3<span>y2</span>y′-18xy′=18y</span></span>Since <span><span>3<span>x2</span></span><span>3<span>x2</span></span></span> does not contain the variable to solve for, move it to the right side of the equation by subtracting <span><span>3<span>x2</span></span><span>3<span>x2</span></span></span> from both sides.<span><span>3<span>y2</span>y'−18xy'=−3<span>x2</span>+18y</span><span>3<span>y2</span>y′-18xy′=-3<span>x2</span>+18y</span></span>Factor <span><span>3y'</span><span>3y′</span></span> out of <span><span>3<span>y2</span>y'−18xy'</span><span>3<span>y2</span>y′-18xy′</span></span>.Tap for fewer steps...Factor <span><span>3y'</span><span>3y′</span></span> out of <span><span>3<span>y2</span>y'</span><span>3<span>y2</span>y′</span></span>.<span><span>3y'<span>(<span>y2</span>)</span>−18xy'=−3<span>x2</span>+18y</span><span>3y′<span>(<span>y2</span>)</span>-18xy′=-3<span>x2</span>+18y</span></span>Factor <span><span>3y'</span><span>3y′</span></span> out of <span><span>−18xy'</span><span>-18xy′</span></span>.<span><span>3y'<span>(<span>y2</span>)</span>+3y'<span>(−6x)</span>=−3<span>x2</span>+18y</span><span>3y′<span>(<span>y2</span>)</span>+3y′<span>(-6x)</span>=-3<span>x2</span>+18y</span></span>Factor <span><span>3y'</span><span>3y′</span></span> out of <span><span>3y'<span>y2</span>+3y'<span>(−6x)</span></span><span>3y′<span>y2</span>+3y′<span>(-6x)</span></span></span>.<span><span>3y'<span>(<span>y2</span>−6x)</span>=−3<span>x2</span>+18y</span><span>3y′<span>(<span>y2</span>-6x)</span>=-3<span>x2</span>+18y</span></span>Divide each term by <span><span><span>y2</span>−6x</span><span><span>y2</span>-6x</span></span> and simplify.Tap for fewer steps...Divide each term in <span><span>3y'<span>(<span>y2</span>−6x)</span>=−3<span>x2</span>+18y</span><span>3y′<span>(<span>y2</span>-6x)</span>=-3<span>x2</span>+18y</span></span> by <span><span><span>y2</span>−6x</span><span><span>y2</span>-6x</span></span>.<span><span><span><span>3y'<span>(<span>y2</span>−6x)</span></span><span><span>y2</span>−6x</span></span>=−<span><span>3<span>x2</span></span><span><span>y2</span>−6x</span></span>+<span><span>18y</span><span><span>y2</span>−6x</span></span></span><span><span><span>3y′<span>(<span>y2</span>-6x)</span></span><span><span>y2</span>-6x</span></span>=-<span><span>3<span>x2</span></span><span><span>y2</span>-6x</span></span>+<span><span>18y</span><span><span>y2</span>-6x</span></span></span></span>Reduce the expression by cancelling the common factors.Tap for more steps...<span><span>3y'=−<span><span>3<span>x2</span></span><span><span>y2</span>−6x</span></span>+<span><span>18y</span><span><span>y2</span>−6x</span></span></span><span>3y′=-<span><span>3<span>x2</span></span><span><span>y2</span>-6x</span></span>+<span><span>18y</span><span><span>y2</span>-6x</span></span></span></span>Simplify the right side of the equation.Tap for more steps...<span><span>3y'=−<span><span>3<span>(<span>x2</span>−6y)</span></span><span><span>y2</span>−6x</span></span></span><span>3y′=-<span><span>3<span>(<span>x2</span>-6y)</span></span><span><span>y2</span>-6x</span></span></span></span>Divide each term by <span>33</span> and simplify.Tap for fewer steps...Divide each term in <span><span>3y'=−<span><span>3<span>(<span>x2</span>−6y)</span></span><span><span>y2</span>−6x</span></span></span><span>3y′=-<span><span>3<span>(<span>x2</span>-6y)</span></span><span><span>y2</span>-6x</span></span></span></span> by <span>33</span>.<span><span><span><span>3y'</span>3</span>=−<span><span><span>3<span>(<span>x2</span>−6y)</span></span><span><span>y2</span>−6x</span></span>3</span></span><span><span><span>3y′</span>3</span>=-<span><span><span>3<span>(<span>x2</span>-6y)</span></span><span><span>y2</span>-6x</span></span>3</span></span></span>Reduce the expression by cancelling the common factors.Tap for more steps...<span><span>y'=−<span><span><span>3<span>(<span>x2</span>−6y)</span></span><span><span>y2</span>−6x</span></span>3</span></span><span>y′=-<span><span><span>3<span>(<span>x2</span>-6y)</span></span><span><span>y2</span>-6x</span></span>3</span></span></span>Simplify the right side of the equation.Tap for more steps...<span><span>y'=−<span><span><span>x2</span>−6y</span><span><span>y2</span>−6x</span></span></span><span>y′=-<span><span><span>x2</span>-6y</span><span><span>y2</span>-6x</span></span></span></span>Replace <span><span>y'</span><span>y′</span></span> with <span><span><span>dy</span><span>dx</span></span><span><span>dy</span><span>dx</span></span></span>.<span><span><span>dy</span><span>dx</span></span>=−<span><span><span><span>x2</span>−6y</span><span><span>y2</span>−6x</span></span></span></span>
The mass of radioactive material remaining after 50 years would be 48.79 kilograms
<h3>How to determine the amount</h3>
It is important to note that half - life is the time it takes for the amount of a substance to reduce by half its original size.
Given the radioactive decay formula as
m(t)=120e−0.018t
Where
t= 50 years
m(t) is the remaining amount
Substitute the value of t
Find the exponential value
m(t) = 48.788399
m(t) = 48.79 kilograms to 2 decimal places
Thus, the mass of radioactive material remaining after 50 years would be 48.79 kilograms
Learn more about half-life here:
brainly.com/question/26148784
#SPJ1
Answer:
C; 13
Step-by-step explanation:
pythagorean theorem. 12^2+5^2=c^2
144+25 = c^2
169 = c^2
13 = c
