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find the expression cot9+cot27+cot63+cot81
2 years ago

Shubham Kamleshbhai Patel
59 Points

In this case u need grouping.

=> (cot 9° + cot 81°) + (cot 27° + cot 63°)
Convert cot to sin and cos

=> [(cos 9° / sin 9°) + (cos 81° / sin 81°)] + [(cos 27° / sin 27°) + (cos 63° / sin 63°)]
Using cross-multiplication,
=>[(sin 81° . cos 9° + cos 81° . sin 9°)/(sin 9° . sin 81°)] + [(sin 63°. cos 27° + cos 63° . sin 27°)/(sin 27° . sin 63°)]

Solving it, u will get the answer as 4√5.
2 years ago
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