Prove that:
sin (70°+θ) — cos (20° — θ) = 0
Consider L.H.S.
= sin (70°+θ) — cos (20° — θ)
= sin (70°+θ) — cos [90°-(70° + θ)]
= sin (70°+θ) — sin (70° + θ)
= 0 = R.H.S.
Hence, proved.