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Core 4 question

Right well im stuck on a volume of revolution question, i have to integrate ((10cos(x-alpha))^2 but i dont know how to actually square that.
Apparently the answer of ((10cos(x-alpha))^2 is 100*0.5(1+cos(2x-2alpha))

any one able to show me how to get to that please?

Reply 1

Ben121

Think about what you get if you do (2x)^2
Apply the same to (10cos(x-a))^2

Reply 2

Sheldon

Original post by Ben121

Think about what you get if you do (2x)^2
Apply the same to (10cos(x-a))^2

That does not help!!

Reply 3

Ben121

It should do
(2x)^2 is 4x^2. You square both parts inside.
Doing that with your expression gives you (100 * cos(x-a)^2)
You can then use an identity to rewrite cos(x-a)^a and integrate.

Reply 4

Sheldon

Original post by Ben121

It should do
(2x)^2 is 4x^2. You square both parts inside.
Doing that with your expression gives you (100 * cos(x-a)^2)
You can then use an identity to rewrite cos(x-a)^a and integrate.