Evaluate the following: 80^ 20^ + 80^ 20^ - Vidyadip

Question

Evaluate the following:
$\cos80^\circ\cos20^\circ+\sin80^\circ\sin20^\circ$

✓

Answer

$=\cos(80^\circ-20^\circ)$$[\cos(\text{A-B})=\cos\text{A}\cos\text{B}+\sin\text{A}\sin\text{B}]$
$=\cos60^\circ$
$=\frac{1}{2}$

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