Answer:
The lifeguard should run across the shore a distance of 48.074 m before jumpng into the water in order to minimize the time to reach the child.
Step-by-step explanation:
This is a problem of optimization.
We have to minimize the time it takes for the lifeguard to reach the child.
The time can be calculated by dividing the distance by the speed for each section.
The distance in the shore and in the water depends on when the lifeguard gets in the water. We use the variable x to model this, as seen in the picture attached.
Then, the distance in the shore is d_b=x and the distance swimming can be calculated using the Pithagorean theorem:
Then, the time (speed divided by distance) is:
To optimize this function we have to derive and equal to zero:
![\dfrac{dt}{dx}=\dfrac{1}{4}+\dfrac{1}{1.1}(\dfrac{1}{2})\dfrac{2x-120}{\sqrt{x^2-120x+5200}} \\\\\\\dfrac{dt}{dx}=\dfrac{1}{4} +\dfrac{1}{1.1} \dfrac{x-60}{\sqrt{x^2-120x+5200}} =0\\\\\\ \dfrac{x-60}{\sqrt{x^2-120x+5200}} =\dfrac{1.1}{4}=\dfrac{2}{7}\\\\\\ x-60=\dfrac{2}{7}\sqrt{x^2-120x+5200}\\\\\\(x-60)^2=\dfrac{2^2}{7^2}(x^2-120x+5200)\\\\\\(x-60)^2=\dfrac{4}{49}[(x-60)^2+40^2]\\\\\\(1-4/49)(x-60)^2=4*40^2/49=6400/49\\\\(45/49)(x-60)^2=6400/49\\\\45(x-60)^2=6400\\\\](https://tex.z-dn.net/?f=%5Cdfrac%7Bdt%7D%7Bdx%7D%3D%5Cdfrac%7B1%7D%7B4%7D%2B%5Cdfrac%7B1%7D%7B1.1%7D%28%5Cdfrac%7B1%7D%7B2%7D%29%5Cdfrac%7B2x-120%7D%7B%5Csqrt%7Bx%5E2-120x%2B5200%7D%7D%20%5C%5C%5C%5C%5C%5C%5Cdfrac%7Bdt%7D%7Bdx%7D%3D%5Cdfrac%7B1%7D%7B4%7D%20%2B%5Cdfrac%7B1%7D%7B1.1%7D%20%5Cdfrac%7Bx-60%7D%7B%5Csqrt%7Bx%5E2-120x%2B5200%7D%7D%20%3D0%5C%5C%5C%5C%5C%5C%20%20%5Cdfrac%7Bx-60%7D%7B%5Csqrt%7Bx%5E2-120x%2B5200%7D%7D%20%3D%5Cdfrac%7B1.1%7D%7B4%7D%3D%5Cdfrac%7B2%7D%7B7%7D%5C%5C%5C%5C%5C%5C%20x-60%3D%5Cdfrac%7B2%7D%7B7%7D%5Csqrt%7Bx%5E2-120x%2B5200%7D%5C%5C%5C%5C%5C%5C%28x-60%29%5E2%3D%5Cdfrac%7B2%5E2%7D%7B7%5E2%7D%28x%5E2-120x%2B5200%29%5C%5C%5C%5C%5C%5C%28x-60%29%5E2%3D%5Cdfrac%7B4%7D%7B49%7D%5B%28x-60%29%5E2%2B40%5E2%5D%5C%5C%5C%5C%5C%5C%281-4%2F49%29%28x-60%29%5E2%3D4%2A40%5E2%2F49%3D6400%2F49%5C%5C%5C%5C%2845%2F49%29%28x-60%29%5E2%3D6400%2F49%5C%5C%5C%5C45%28x-60%29%5E2%3D6400%5C%5C%5C%5C)
As 
, the lifeguard should run across the shore a distance of 48.074 m before jumpng into the water in order to minimize the time to reach the child.
Answer:
7a 3 −7a+1
Step-by-step explanation: I hope this help.
STEP
1
:
Equation at the end of step 1
((7a3 - 2a) - 2) + (3 - 5a)
STEP
2
:
Polynomial Roots Calculator :
2.1 Find roots (zeroes) of : F(a) = 7a3-7a+1
Polynomial Roots Calculator is a set of methods aimed at finding values of a for which F(a)=0
Rational Roots Test is one of the above mentioned tools. It would only find Rational Roots that is numbers a which can be expressed as the quotient of two integers
The Rational Root Theorem states that if a polynomial zeroes for a rational number P/Q then P is a factor of the Trailing Constant and Q is a factor of the Leading Coefficient
In this case, the Leading Coefficient is 7 and the Trailing Constant is 1.
The factor(s) are:
of the Leading Coefficient : 1,7
of the Trailing Constant : 1
Let us test ....
P Q P/Q F(P/Q) Divisor
-1 1 -1.00 1.00
-1 7 -0.14 1.98
1 1 1.00 1.00
1 7 0.14 0.02
Polynomial Roots Calculator found no rational roots
Final result :
7a3 - 7a + 1
Answer:
4 ft.
Step-by-step explanation:
We can consider the orignial square's sides to be x, so area of the original figure: 
The new rectangle's sides will be x and x+8, so the area of the new figure will be x^2+8x.
We know that the new area is 3 times the old one. So our equation will be:
x^2+8x=3x^2
our answer will be x=4.
Therfore, the length of the side of the old flower bed is 4 ft.
Answer:
x=8
Step-by-step explanation:
First multiply 30 and 16 to find out how many ounces are in the 30 lb. bag of dog food.
30 x 16=480
Since the 3 dogs eat 20 ounces of food, we can make a equation.
3(20x)=480
20 x 3=60
60x=480
x=8
<u>Final answer</u>
8 days
Answer:
a = 9
Step-by-step explanation:
2(a + 7) = 5a - 13
We want to bring a to one side, I will choose to bring it to the right
First, expand the bracket by multiplying 2 with a + 7
2a + 14 = 5a - 13
Bring the -13 to the left by adding 13 to both sides
2a + 14 + 13 = 5a - 13 + 13
Simplify
2a + 27 = 5a
Bring the 2a to the right by subtracting 2a from both sides
2a - 2a + 27 = 5a - 2a
Simplify
27 = 5a - 2a
27 = 3a
Bring the 3 to the left by dividing both sides by 3
27÷3 = a
Simplify
a = 9
