Question

# Find the value of $\cos \theta$,If angle $\theta =-30{}^\circ$

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Hint: Here we are given angle $\theta =-30{}^\circ$ and we have to find the value of $\cos \theta$ . So for that substitute the value of $\theta =-30{}^\circ$ in $\cos \theta$. Try it, you will get the answer.

The cosine function, along with sine and tangent, is one of the three most common trigonometric functions. In any right triangle, the cosine of an angle is the length of the adjacent side (A) divided by the length of the hypotenuse (H). In a formula, it is written simply as '$\cos$'. $\cos$ function (or cosine function) in a triangle is the ratio of the adjacent side to that of the hypotenuse. The cosine function is one of the three main primary trigonometric functions and it is itself the complement of sine (cos + sine).
The cosine graph or the cos graph is an up-down graph just like the sine graph. The only difference between the sine graph and the cos graph is that the sine graph starts from $0$ while the cos graph starts from $90{}^\circ$ (or $\dfrac{\pi }{2}$).
We are given angle $\theta =-30{}^\circ$ .
So now we have to find $\cos \theta$ .
Let us substitute the value $\theta =-30{}^\circ$ in $\cos \theta$, we get,
$\cos \theta =\cos (-30{}^\circ )$
We know that, $\cos (-a)=\cos a$.
$\cos \theta =\cos (-30{}^\circ )=\cos 30{}^\circ =\dfrac{\sqrt{3}}{2}$
Here, we get the value of $\cos \theta$ at $\theta =-30{}^\circ$ is $\dfrac{\sqrt{3}}{2}$ .