Consider L.H.S.

= (sec 70° sin 20°) + (cos 20° cosec 70°)

= (sec (90-20)° sin 20°) + (cos 20° cosec (90-20)°)

= (cosec 70° sin70°) + (cos 20° sec 20°)

= 1 + 1 (∵ cosec θ = 1/sinθ and sec θ = 1/cos θ )

= 2 = R.H.S.

Hence, proved.