Question

What is cotangent 135?

Answer 1

Hint: We explain the process of finding values for associated angles. We find the rotation and the position of the angle for ${{135}^{\circ }}$. We explain the changes that are required for that angle. Depending on those things we find the solution.

Complete step by step solution:
We need to find the ratio value for $\cot 135$.
For general form of $\cot \left( x \right)$, we need to convert the value of x into the closest multiple of $\dfrac{\pi }{2}$ and add or subtract a certain value $\alpha $ from that multiple of $\dfrac{\pi }{2}$ to make it equal to x.
Let’s assume $x=k\times \dfrac{\pi }{2}+\alpha $, $k\in \mathbb{Z}$. Here we took the addition of $\alpha $. We also need to remember that $\left| \alpha \right|\le \dfrac{\pi }{2}$.
Now we take the value of k. If it’s even then keep the ratio as cot and if it’s odd then the ratio changes to tan ratio from cot.
Then we find the position of the given angle as quadrant value measured in counter clockwise movement from the origin and the positive side of X-axis.
If the angel falls in the first or third quadrant then the sign remains positive but if it falls in the second or fourth quadrant then the sign becomes negative.
Depending on the sign and ratio change the final angle becomes $\alpha $ from x.
The final form becomes $\cot 135=\cot \left( 1\times \dfrac{\pi }{2}+45 \right)=-\tan \left( 45 \right)=-1$.
Therefore, the value of $\cot 135$ is $-1$.
So, the correct answer is “$-1$.”.

Note: We need to remember that the easiest way to avoid the change of ratio thing is to form the multiple of $\pi $ instead of $\dfrac{\pi }{2}$. It makes the multiplied number always even. In that case we don’t have to change the ratio. If $x=k\times \pi +\alpha =2k\times \dfrac{\pi }{2}+\alpha $. Value of $2k$ is always even.