Q2 of 54 Page 312

Without using trigonometric tables, prove that:
(sin 65° + cos 25°)(sin 65° - cos 25°) = 0

Consider (sin 65° + cos 25°)(sin 65° - cos 25°)

= sin2 65° - cos2 25°


= sin2 65° - cos2 (90 - 65)°


= sin2 65° - sin2 65°


= 0


Hence, proved.


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