TriG QueStiOn.. (1 Viewer)

[+GriM ReApeR+]

Q. a) Find an expression for sin^2x in terms of cos2x.
b) Hence find the exact volume of the solid if the curve y=sinx is rotated about the x-axis from x=0 to x=pi/4.

I cant get part a) (actually..could'nt be bothered to )

Thanks

 

[Heinz]

a) Find an expression for sin^2x in terms of cos2x.

rearrange the double angle formula for cos2x to get sin^2x = (1-cos2x)/2

b) V = pi times the integral of (sin^2x) between x = 0 and x = pi/4

Sub in the result from part a so you can integrate it.

You have to be bothered doing part a if you want to get part b out. This is a standard question worth about 3 marks in the HSC.

 

[kpq_sniper017]

i have to agree with heinz.
it's an easy 3 marks? so why not do it?

use: cos2x = 1 - 2sin²x
then rearrange that to get sin²x = ???