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Question : 23 of 160
Marks:
+1,
-0
Solution:
cos4‌+cos4‌+cos4‌+cos4‌ +cos4‌+cos4‌+cos4‌+cos4‌ =(cos4‌+cos‌)+(cos4‌+cos4‌) ‌‌+(cos4‌+cos4‌)+(cos4‌+cos4‌) =(2cos4‌+2cos4‌+2cos4‌)+cos4‌+cos4(π) =2[cos4‌+cos4(‌−‌)+cos4‌]+0+1 =2(cos4‌+sin4‌+‌)+1 =2{(cos2‌+sin2‌)2−2sin2‌cos2‌+‌}+1 =2{1−2‌sin‌cos2‌+‌}+1 =2−(2‌sin‌cos‌)2+‌+1=3−(‌)2+‌ =3
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