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# If $\sin x = \cos x$ and x is acute state the value of x in degrees

Last updated date: 24th Jun 2024
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Hint: We have been given a trigonometric equation, by making certain changes to it and using various trigonometric identities, we can easily obtain the required value of angle x. This angle x is given to be acute, which means its value is less than 90°.
Trigonometric identities to be used:
${\sin ^2}x + {\cos ^2}x = 1 \\ \sin 2x = 2\sin x\cos x \;$

We have been given an equation:
$\sin x = \cos x$ and we need to find the value of angle x in degrees.
This equation can be written as:
$\sin x - \cos x = 0$
Squaring both the sides, we get:
${\left( {\sin x - \cos x} \right)^2} = 0 \\ {\sin ^2}x + {\cos ^2}x - 2\sin x\cos x = 0 \\ 1 - 2\sin x\cos x = 0\left( {\because {{\sin }^2}x + {{\cos }^2}x = 1} \right) \; 1 = 2\sin x\cos x \;$
The value of double sine angle is given as:
$\sin 2x = 2\sin x\cos x$
Substituting this value, we get:
$\sin 2x = 1$
The value of sin 90° is 1, so the above equation can be written as:
$\sin 2x = \sin {90^\circ } \\ \Rightarrow 2x = {90^\circ } \\ \therefore x = {45^\circ } \;\$
It is given that the angle is acute i.e. less than 90° which is also true for the angle obtained.
Therefore, if $\sin x = \cos x$ and x is acute then the value of x is 45 degrees
So, the correct answer is “ 45° ”.

Note: We can also find the value of angle x by the following method, using the basic formula for tanx i.e. $\dfrac{{\sin x}}{{\cos x}} = \tan x$
Given equation: $\sin x = \cos x$
Dividing both the sides by $\cos x$ , we get:
$\dfrac{{\sin x}}{{\cos x}} = \dfrac{{\cos x}}{{\cos x}} \\ \tan x = 1 \\ \left( {\because \dfrac{{\sin x}}{{\cos x}} = \tan x} \right) \\$
The value of tan is 1 when the angle is equal to 45°, x can be calculated mathematically as:
$\tan x = 1 \\ \Rightarrow x = {\tan ^{ - 1}}(1) \\ \therefore x = {45^\circ }\left( {\because \tan {{45}^\circ } = 1} \right) \;$
Thus, we get the value of x as 45° by following every method.
The angles less than 90° are called acute angles and greater than that are called obtuse.