If sintheta=sqrt403/22sinθ=40322 and pi/2<theta<piπ2<θ<π, how do you find tan2thetatan2θ?

1 Answer
Nov 20, 2016

tan2theta=(9sqrt403)/161tan2θ=9403161

Explanation:

If theta in [pi/2,pi]θ[π2,π], costheta<0cosθ<0, so:
costheta=-sqrt{1-sin^2theta}cosθ=1sin2θ
costheta=-sqrt{1-403/484}=-sqrt{81/484}=-9/22cosθ=1403484=81484=922

tantheta=sintheta/costheta=(sqrt{403}/22)/(-9/22)=-sqrt403/9tanθ=sinθcosθ=40322922=4039
tan2theta=(2tantheta)/(1-tan^2theta)=(-(2sqrt403)/9)/(1-403/81)=(-(2sqrt403)/9)/(-322/81)=(9sqrt403)/161tan2θ=2tanθ1tan2θ=24039140381=2403932281=9403161