Question

Evaluate. cos(-780°)

Answer 1

0.5 is the answer of cos- 780 °

Answer 2

$\cos(-780)=\dfrac{1}{2}$

Step-by-step explanation:

We have,

$\cos(-780)$

To find, the value of $\cos(-780)=?$

∴ $\cos(-780)$

$=\cos 780$

[ ∵ $\cos(-A) =\cos A$]

$=\cos (2\times 360+60)$

$=\cos 60$ [Since, first quadrant]

$=\dfrac{1}{2}$

Hence, $\cos(-780)=\dfrac{1}{2}$