Question

if cosa-sina=1 then prove that cosa + tana =+-1

Answer 1

cos(a)+sin(a)=1

squaring both sides

cos2a+sin2a+2sinacosa=1

1−sin2a+1−cos2a+2sinacosa=1. (usingsin2+cos2=1

2−sin2a−cos2a+2cosasina=1

sin2a+cos2−2cosasina=1

(cosa−sina)2=1

cosa−sina=+−1......

Hope it helps ☺️