Originally Posted by
SarahGr I have one more question for you guys here's what I was given
Suppose sinα = 4/5 and tanβ= -3/4 where π/2 < α < β < π (pi)
the above inequality tells you the quadrant where α and β both reside.
Find:
Sin(α + β)
Cos(α + β)
Tan(α + β)
Sin2α
Cos2β
Tan2α
What i have been doing is figuring out the other trig functions
They gave me sinα=4/5 and tanβ=-3/4
the signs of your trig values below were all incorrect ... α and β are both quadrant II angles ... sine is positive, cosine and tangent are negative.
note the changes ...
from that i found cosα = -3/5 tanα = -3/4 and sinβ = +3/5 cosβ = -4/5
I tried problem a ... redo it
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? understand now? =/