How do you evaluate $cos (- 315)$ $cos(-315)$ ?

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Answer 1 · 2015-02-12T11:38:42

Since all trig functions are periodic, we may add multiples of $360^{0}$ $360^0$ (in the tangent function even multiples of $180^{0}$ $180^0$ )

So $cos (- 315^{0}) = cos (- 315^{0} + 360^{0}) = {cos 45}^{0}$ $cos(-315^0)=cos(-315^0+360^0)=cos45^0$

An angle of $45^{0}$ $45^0$ means an isosceles right-angled triangle with sides in the ratio $1 - 1 - \sqrt{2}$ $1-1-sqrt2$

The cosine of the angle will then be $\frac{1}{\sqrt{2}} = \frac{1}{2} \sqrt{2} \approx 0.707$ $1/sqrt2=1/2 sqrt2~~0.707$

How do you evaluate cos(-315)cos(−315)cos(-315)?