How do you solve the equation #sec^2theta-2sectheta-3=0# for #[-180^circ, 180^circ)#?

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Answer 1 · 2017-02-05T14:29:00

#theta= +-70.55, +-180#

#sec^2theta -2sectheta -3 =0#

Let #x=sectheta#

#x^2 -2x -3 =0#

#(x-3)(x+1) =0#

#x=3#

#x=-1#

#sectheta=3#

#costheta = 1/3#

#theta = 70.55, -70.55#

#costheta = -1#

#theta = 180, -180#