Surface Area Calculus

[rotund prawn]

y = 7x, -1 <= x <= 1, about x axis. Find surface area. Why does solving this in a usual manner results to 0, (which is the actual answer is not)

[chilly steppe]

Whats the correct answer tho?

The answer id 70pieroot2?

[rotund prawn]

Yes

[chilly steppe]

Do integration by parts, instead of doing -1 to 1 directly do it by parts

Split it to -1 to 0 and 0 to 1

[rotund prawn]

Yeah i get it now, i think 0 to 1, times 2 to the whole answer still works. But its easy to mess this up, specially with this simple looking problems

[chilly steppe]

Not really, its just because the limits in this question favors the situation

But -xdx is the actual thing

So beware

[languid cobalt]

I would recommend not calling this method "integration by parts", because that means a different method entirely.

[chilly steppe]

Yeah mb, I realised thats a whole different thing

Splitting is what we can call it