Asked by Anonymous

cotθ=3, cos<0. Find the exact value of sin θ/2 using half-angle formula. Please help!
Answered by Steve
if cot > 0 and cos < 0, then you are in QIII

cotθ = 3
cosθ = -3/√10

sin θ/2 = √((1-cosθ)/2)
= √((1+3/√10)/2)

Note that since θ is in QIII, θ/2 is in QII, and so sinθ is positive.
Answered by Anonymous
WOW!! Thanks so much! Looks like I knew how to solve it the whole time, just needed to see the proof I guess
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