cos φ = 4/5 with 0°

Question

cos φ = 4/5 with 0° < φ < 90°
(a)    sin 2φ

anonymous · Answer

how do you solve this??

anonymous · Answer

i know the answe is 24/25

anonymous · Answer

how do you know the answer is 24/25? and what's with the a) (sin 2phi) ?

anonymous · Answer

the a has no part in it

anonymous · Answer

okay so do you want me to solve this algebraically or tell you how to solve it with a calulator?

anonymous · Answer

actually i don't know if i know how to do with without a calculator lol

anonymous · Answer

sin2phi=2sinphicosphi
we are given cosphi=4/5
then sinphi=3/5
sin2phi=2*4/5*3/5=24/25

anonymous · Answer

cos φ = 4/5 with 0° < φ < 90°
(a)    sin 2φ
lemme just use x instead of phi...
sin2x = 2sinxcosx by the double angle formula..
Look at this triangle...
|dw:1331633449765:dw|
this triangle is made according to the given..
So sin2x=2*(3/5)*(4/5)=24/25