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# Trig watch

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1. x = theta

given that pi < x < 3pi/2, find value of tan x/2 when tanx = 3/4

2. from scratch. it's not like anyone learns these things...

cosA = 2cos^2 A/2 - 1 = 1 - 2sin^2 A/2
cosA/2 = rt((1+cosA)/2), sinA/2 = rt((1-cosA)/2)

so tanA/2 = rt((1-cosA)/(1+cosA))

oh look, 3,4,5 triangle alert. cosA = 4/5

tanA/2 = rt((1/5)/(9/5)) = rt(1/9) = 1/3

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Updated: October 17, 2006
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