If prove that
Given: sin θ – cos θ = 1 …….(1)
cos θ + sin θ = 1 …….(2)
Square equation (1) and (2) on both sides:
sin2 θ + cos2 θ – 2 cos θ sin θ = 1 …….(3)
cos2 θ + sin2 θ + 2 cos θ sin θ = 1 ……..(4)
Add equation (3) and (4):
(sin2 θ + cos2 θ) + (sin2 θ + cos2 θ) = 1+1
⇒ (1) + (1) = 2
⇒ + = 2
Hence, proved.