Question

how to do: cos(2a)=-sin(a) with 0 14 years ago

Answer 1

i believe you mean pi and not pie
-sin(a)=-cos(pi/2-a)
or
sin(-a)=cos(pi/2+a)

so we have
cos(2a)=cos(pi/2+a)

\[2a=\frac{\pi}{2}+a =>a=\frac{\pi}{2}\]
so that is one value that works

Answer 2

there is another way to go about it

Answer 3

i see three intersections in my calculator
all i can get is just pi/2 so let me think of another way

Answer 4

sin(a)=1 when a=pi/2
sin(a)=-1/2 when a=7pi/6 or 11pi/6

Answer 5

three values! :)

Answer 6

very cool!

Answer 7

:)

Answer 8

@myininaya plz help
http://openstudy.com/groups/mathematics#/groups/mathematics/updates/4e7147e60b8bbc8fb32c09c6