How to solve?

A small open cylindrical glass container has a radius of r cm as shown in the diagram.
The total surface area (A), expressed in terms of r, is found to be
A(r) = 80/r + πr^2
Find the radius of the cylinder so that the surface area (A) is at a minimum.
Give your answer correct to 2-decimal places.

A small open cylindrical glass container has a radius of r cm as shown in the diagram.
The total surface area (A), expressed in terms of r, is found to be
A(r) = 80/r + πr^2
Find the radius of the cylinder so that the surface area (A) is at a minimum.
Give your answer correct to 2-decimal places.

Differentiate first with. The formula find r when = 0 sub r into second derivative .

Thank you, I was stuck on it for minutes.
Now I’ve done it!
Look:

Thank you, I was stuck on it for minutes.
Now I’ve done it!
Look:

Congrats what did u get in ur GCSEs ?

Looks good. Id be careful of rounding to 2dp during the working as they want the ans to 2dp and sometimes you can lose accuracy in the calcs

Yeah true I was just so excited to solve it that I forgot to. But anyways how did u realise it was differentiation was it becuase of the minimum?

A minimum is one type of stationary point, so when the gradient (derivative) is zero.