# Thread: surface area calculation using differntials, Help plz

1. ## surface area calculation using differntials, Help plz

The surface area of a cone with radius r and height h is given by the formula:a= pi r^2 + pi r sqr(pi ^2 + h^2) . A particular cone has a radius of 3 cm and a height of 8 cm. a) Use differentials to estimate how much the surface area would increase if only the radius was increased by 0.2 cm.b)Use differentials to estimate how much the surface area would increase if only the height was increased by 0.2 cm.

2. $A=\pi r^2 + \pi r \sqrt{\pi^2 + h^2}$

Then the differential is:

$dA=A'_r dr + A'_h dh$

Determine the partial derivatives, and then use the values for dr and dh that are given (i.e., $dr=0.2$ [cm] in the first case).