If theta in [pi/2,pi]θ∈[π2,π], costheta<0cosθ<0, so:
costheta=-sqrt{1-sin^2theta}cosθ=−√1−sin2θ
costheta=-sqrt{1-403/484}=-sqrt{81/484}=-9/22cosθ=−√1−403484=−√81484=−922
tantheta=sintheta/costheta=(sqrt{403}/22)/(-9/22)=-sqrt403/9tanθ=sinθcosθ=√40322−922=−√4039
tan2theta=(2tantheta)/(1-tan^2theta)=(-(2sqrt403)/9)/(1-403/81)=(-(2sqrt403)/9)/(-322/81)=(9sqrt403)/161tan2θ=2tanθ1−tan2θ=−2√40391−40381=−2√4039−32281=9√403161