Originally Posted by

**sinewave85** I can't seem to get the right answer to this one, and I hope someone can tell me what I am doing wrong!

"You measure the radius of a circle to be 12 cm and use the formula A = pi(r^2) to calculate the area. If your measurement of the radius is accurate to within 3%, approximately how accurate (to the nearest percent) is your calculation of the area?

$\displaystyle A(r) = \pi r^2$

$\displaystyle A'(r) = 2\pi r$

$\displaystyle \left|\frac{dA}{A}\right|= \left|\frac{2 \pi r dr}{ \pi r^2}\right|$

$\displaystyle \left|\frac{dA}{A}\right| = 2\left|\frac{dr}{r}\right|$