Cot 70+4cos70. Derive the solution...
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Cot 70+4cos70
= 5cos70
But, I think your question is " cos70+ cos40 "
We know that, cosC + cosD = 2 cos(C+D/2) cos(C-D/2)
cos70+ cos40
= 2 cos(70+40/2) cos(70-40/2)
= 2 cos55° cos15°
= 5cos70
But, I think your question is " cos70+ cos40 "
We know that, cosC + cosD = 2 cos(C+D/2) cos(C-D/2)
cos70+ cos40
= 2 cos(70+40/2) cos(70-40/2)
= 2 cos55° cos15°
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