Question

Sin 20° cos 70° + cos 20° sin 70° = 1​

Answer 1

Using three

identify that is

• sin = (cos90 - ∅)
• Cos = ( sin90 - ∅)
• Sin²A + Cos²A = 1

= Cos(90 - 20) Cos70 + Sin ( 90 - 20 )

Sin70 = 1

= Cos70 Cos70 + Sin70 Sin70 = 1

now using Sin²A + Cos²A = 1

= Cos²70 + Sin²70 = 1

Hence it is proved.

Answer 2

see the attachment... .