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## Homework Statement

Suppose sinα = 4/5 and tanβ= -3/4 where π/2 < α < β < π (pi)

Find:

Sin(α + β)

Cos(α + β)

Tan(α + β)

Sin2α

Cos2β

Tan2α

## The Attempt at a Solution

What i have been doing is figuring out the other trig functions

They gave me sinα=4/5 and tanβ=-3/4

from that i found cosα=3/5 tanα=3/4 and sinβ=-3/5 cosβ=4/5

I tried problem a

sin(α+β)=sinαcosβ+cosαsinβ

sin(α+β)=4/5 * 4/5 + 3/5 * -3/5

which gives me 7/25 but I'm not sure I am doing this right... what is the whole (π/2 < α < β < π) thing about am I supposed to be finding points on the unit circle or something? =/