I need help, I have algebra 1

Question

So this is the question. "In the formula for surface area of a sphere S=4pir^2 , solve for r."

I emailed my teacher for help she said to get the r by its self. And I have this problem in Get More Math and the answer should be "R= then a number here but do decimals."

Answer 1

Hello, Cinthia,

I can understand your frustration. Let's see how we can make sense of what is requested.

The formula for the surface area of a sphere, as you point out, is 4πr² . You were told to isolate r, which means rearrange the equation so that r is on one side and the rest of the critters (metric term for terms) are on the other. Let's try doing that for the full equation:

A = 4πr²

Divide both sides by 4π:

A/4π = r²

Then take the square root of both sides and switch them around so that r is on the left:

r = [A/4π]^1/2

I can't make a good square root sign in this message box, but that's what the []^1/2 means.

The equation is mathematically the same as before. but now written in a format that tells us directly what r is equal to. A typical problem where this might be useful is when you are given the surface area of a sphere and are asked what is its radius. Presto - just divide the area by 4π and take the square root of the result.

I'm not sure which aspect of the problem is most confusing nor how much algebra you've had so far. Let me know if there is something else I could help explain.

Explore on your own at: https://www.mathsisfun.com/geometry/sphere-volume-area.html

I hope this helps,

Bob

Answer 2

SA = 4 π r²

^

Solving for r we get:

r = √(SA / 4π)

If you plug in a given surface area, you can solve for the corresponding r value.