23. If sinA + sinA = 1, then find cos A +cos'A.
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✒Given :
⟶sinØ+ sin²2Ø =1.
✒To find :-
⟶ cos² Ø + cos4 Ø.
✒ Solution :-
We have,
°. sinØ + sin²Ø = 1
⟹ sin Ø = 1 - sin²Ø
⟹ sin Ø = cos² Ø
[ Squaring both side ]
⟹ sin²Ø = cos4Ø ____________(i).
✒Now,
°° cos²Ø + cos4 Ø
⟹ cos²Ø + sin²Ø ______________ [Using (i)].
⟹ 1
[sin²Ø + cos²Ø = 1]
proved.
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