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3 years ago

Find the radius of the circle with equation x²+y²+8x+8y+28=0

Mathematics

1 answer:

galina1969 [7]3 years ago

3 0

<h2>Hello!</h2>

The answer is:

Center: (-4,-4)

Radius: 2 units.

To solve the problem, using the given formula of a circle, we need to find its standard equation form which is equal to:

$(x-h)^{2}+(y-k)^{2}=r^{2}$

Where:

"h" and "k" are the coordinates of the center of the circle and "r" is its radius.

So, we need to complete the square for both variable "x" and "y".

The given equation is:

$x^{2}+y^{2}+8x+8y+28=0$

So, solving we have:

$x^{2}+y^{2}+8x+8y=-28$

$(x^2+8x+(\frac{8}{2})^{2})+(y^2+8y+(\frac{8}{2})^{2})=-28+((\frac{8}{2})^{2})++(\frac{8}{2})^{2})\\\\(x^2+8x+16 )+(y^2+8y+16)=-28+16+16\\\\(x^2+4)+(y^2+4)=4$

$(x^2-(-4))+(y^2-(-4))=4$

Now, we have that:

$h=-4\\k=-4\\r=\sqrt{4}=2$

So,

Center: (-4,-4)

Radius: 2 units.

Have a nice day!

Note: I have attached a picture for better understanding.

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Y/−7 = 1 /4 what does y =

Studentka2010 [4]

Answer:

y = - $\frac{7}{4}$

Step-by-step explanation:

$\frac{y}{-7}$ = $\frac{1}{4}$ ( cross- multiply )

4y = - 7 ( divide both sides by 4 )

y = - $\frac{7}{4}$

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3 years ago

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Taxicab Ride

lara [203]

Answer: Carlton's cabs is the cheaper option if she wants to travel 15 miles.

Step-by-step explanation:

A linear relationship can be written as:

c = a*n + b

where a is the slope (in this case, the rate per mile), n is the number of miles driven by the taxi, and b is the y-axis (in this case, the initial cost) intercept.

For a line that passes through the points (x1, y1) and (x2, y2), the slope can be written as:

a = (y2 - y1)/(x2 - x1).

Then for each table we only need to take two points and construct the linear equation:

Treveon's Taxis:

We can use the two points (1, $5.25) and (3, $9.75)

Then the rate per mile, or the slope, will be:

a = ($9.75 - $5.25)/(3 - 1) = $2.25

This means that each mile costs $2.25

Then the equation will be written as:

c = $2.25*n + b

To find the value of b, we can just replace one of the points in the equation. For example, I will se the point (1, $5.25) this means that we need to replace n by 1, and c by $5.25

Then:

$5.25 = $2.25*1 + b

$5.25 - $2.25 = b

$3 = b

Then the initial cost here is $3.

And the equation will be:

c = $2.25*n + $3.

Carlton's Cabs:

Same approach as before, here I will use the points (1, $7.00) and (3, $10.50)

Then the rate per mile will be:

a = ($10.50 - $7.00)/(3 - 1) = $1.75

The rate per mile is $1.75 (is cheaper than in the previous case)

Then at the moment, the equation is:

c = $1.75*n + b

To find the initial cost, we do the same as before, here i will use the point (1, $7.00)

$7.00 = $1.75*1 + b

$7.00 - $1.75 = b

$5.25 = b

The initial cost here is $5.25

And the equation will be:

c = $1.75*n + $5.25

Now, which one is cheaper for 15 miles?

We only need to replace n by 15 in both equations, and see in which one the cost is lower:

Treveon's Taxis:

c(15) = $2.25*15 + $3 = $36.75

Carlton's Cabs:

c(15) = $1.75*15 + $5.25 = $31.5

Then Carlton's Cabs is a better option if you want to travel 15 miles.

6 0

3 years ago

Please help me thank you!

sergiy2304 [10]

Answer:

The equation of the line that passes through the points

(5,2) and (-5,6)

y=-2/5x+4

Step-by-step explanation:

You want to find the equation for a line that passes through the two points:

(5,2) and (-5,6).

First of all, remember what the equation of a line is:

y = mx+b

Where:

m is the slope, and

b is the y-intercept

First, let's find what m is, the slope of the line...

The slope of a line is a measure of how fast the line "goes up" or "goes down". A large slope means the line goes up or down really fast (a very steep line). Small slopes means the line isn't very steep. A slope of zero means the line has no steepness at all; it is perfectly horizontal.

For lines like these, the slope is always defined as "the change in y over the change in x" or, in equation form:

So what we need now are the two points you gave that the line passes through. Let's call the first point you gave, (5,2), point #1, so the x and y numbers given will be called x1 and y1. Or, x1=5 and y1=2.

Also, let's call the second point you gave, (-5,6), point #2, so the x and y numbers here will be called x2 and y2. Or, x2=-5 and y2=6.

Now, just plug the numbers into the formula for m above, like this:

m= 6 - 2/-5 - 5 or m= 4-10 or m=-2/5

So, we have the first piece to finding the equation of this line, and we can fill it into y=mx+b like this:

y=-2/5x+b

Now, what about b, the y-intercept?

To find b, think about what your (x,y) points mean:

(5,2). When x of the line is 5, y of the line must be 2.

(-5,6). When x of the line is -5, y of the line must be 6.

Because you said the line passes through each one of these two points, right?

Now, look at our line's equation so far: y=-2/5x+b. b is what we want, the -2/5 is already set and x and y are just two "free variables" sitting there. We can plug anything we want in for x and y here, but we want the equation for the line that specfically passes through the two points (5,2) and (-5,6).

So, why not plug in for x and y from one of our (x,y) points that we know the line passes through? This will allow us to solve for b for the particular line that passes through the two points you gave!.

You can use either (x,y) point you want..the answer will be the same:

(5,2). y=mx+b or 2=-2/5 × 5+b, or solving for b: b=2-(-2/5)(5). b=4.

(-5,6). y=mx+b or 6=-2/5 × -5+b, or solving for b: b=6-(-2/5)(-5). b=4.

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3 years ago

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Strike441 [17]

Answer:

b = 7√3

Step-by-step explanation:

This 30°- 60°- 90° triangle has the proportions:

side opposite of the 30° angle = x

side opposite of the 60° angle = x√3

side opposite of the 90° angle = 2x

____________________________

Given the side opposite of the 30° angle which is 7 units long, this can be thought of as x. Knowing the proportions of the other sides, we can find b knowing that this is the side opposite of the 60° angle which is x√3.

Since x = 7, x√3 = 7√3, and therefore

b = 7√3.

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nalin [4]

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