Trigonometry Examples

$\cos (- \frac{3}{5}) \cos (\frac{2}{5}) + \sin (\frac{4}{5}) \sin (\frac{\sqrt{21}}{5}) = \frac{6 - 4 \sqrt{21}}{25}$

Step 1

The left side $1.32939616$ does not equal to the right side $- 0.49321211$ , which means that the given statement is false.

False