How do you solve $\sin x - \tan x = 0$?
Answer
627.9k+ views
Hint:A general solution is one which gives all solutions of a given trigonometric equation where n is integer and $n \in Z$.
The above equation can be easily solved by putting the values of the given trigonometric function.
In this question, $\tan x$ can be written in the form of $\sin x$ and $\cos x$.
Complete step by step answer:
We know, $\tan x = \dfrac{{\sin x}}{{\cos x}}$
Putting the value of $\tan x$in $\sin x - \tan x = 0$
$ \Rightarrow \sin x - \dfrac{{\sin x}}{{\cos x}} = 0$
Taking LCM and solving the above equation,
$ \Rightarrow \dfrac{{\sin x\cos x - \sin x}}{{\cos x}} = 0$
By cross multiplication,
$ \Rightarrow \sin x\cos x - \sin x = 0 \cdot \cos x$
$ \Rightarrow \sin x\cos x - \sin x = 0$
Take $\sin x$ common,
$ \Rightarrow \sin x(\cos x - 1) = 0$
A factor should be zero.
$ \Rightarrow \sin x = 0$ or $\cos x - 1 = 0$
$ \Rightarrow \sin x = 0$ or $\cos x = 1$
We know, the general solution of $\sin x = 0$ is $x = n\pi $
and for $\cos x = 1$
We know, $\cos {0^ \circ } = 1$
So, $\cos x = \cos {0^ \circ }$
$ \Rightarrow \cos x = \cos \alpha $
$ \Rightarrow x = 2n\pi \pm \alpha $
Here, $\alpha = {0^ \circ }$
So, $x = 2n\pi \pm 0$
$ \Rightarrow x = 2n\pi $
Thus, $x = n\pi $ or $x = 2n\pi $ , where $n \in Z$ and n is integer.
Additional information:
You can also solve this by taking $\tan x$ to the right-hand side.
$ \Rightarrow \sin x = \tan x$
$ \Rightarrow \sin x = \dfrac{{\sin x}}{{\cos x}}$
$ \Rightarrow \sin x\cos x = \sin x$
Bring $\sin x$ to the left-hand side,
$ \Rightarrow \sin x\cos x - \sin x = 0$
Take $\sin x$ common
$ \Rightarrow \sin x(\cos x - 1) = 0$
Factors should be zero
$ \Rightarrow \sin x = 0$ or $\cos x - 1 = 0$
$ \Rightarrow \sin x = 0$ or $\cos x = 1$
We know, $\cos {0^ \circ } = 1$
So, $\cos x = \cos {0^ \circ }$
$ \Rightarrow \cos x = \cos \alpha $
$ \Rightarrow x = 2n\pi \pm \alpha $
Here, $\alpha = {0^ \circ }$
So, $x = 2n\pi \pm 0$
$ \Rightarrow x = 2n\pi $
Thus, $x = n\pi $ or $x = 2n\pi $ $n \in Z$ and n is integer.
Note: The general solution of $\sin x = 0$ is $x = n\pi $ , general solution of $\cos x = 1$ is $x = 2n\pi $ , general solution of $\cos x = 0$ is $x = (2n + 1)\dfrac{\pi }{2}$ and general solution of $\tan x = 0$ is $x = n\pi $ where $n \in Z$ and n is integer.
Range of $\sin x = [ - 1,1]$ ,domain is all real numbers and period $ = 2\pi $
Range of $\cos x = [ - 1,1]$ ,domain is all real numbers and period $ = 2\pi $
Range of $\tan x = $ all real numbers, domain is $R - (2k + 1)\dfrac{\pi }{2}$ , $k \in Z$, k is integer and R is real number , period $ = \pi $
Always try to reduce the trigonometric equations in simpler functions like $\sin \theta $, $\cos \theta $ to make it easier to solve.
Always bring the right-hand side values to the left-hand side so as to factorize and make the factor zero for each.
Signs of all trigonometric functions should be taken care of for every interval or quadrant.
The above equation can be easily solved by putting the values of the given trigonometric function.
In this question, $\tan x$ can be written in the form of $\sin x$ and $\cos x$.
Complete step by step answer:
We know, $\tan x = \dfrac{{\sin x}}{{\cos x}}$
Putting the value of $\tan x$in $\sin x - \tan x = 0$
$ \Rightarrow \sin x - \dfrac{{\sin x}}{{\cos x}} = 0$
Taking LCM and solving the above equation,
$ \Rightarrow \dfrac{{\sin x\cos x - \sin x}}{{\cos x}} = 0$
By cross multiplication,
$ \Rightarrow \sin x\cos x - \sin x = 0 \cdot \cos x$
$ \Rightarrow \sin x\cos x - \sin x = 0$
Take $\sin x$ common,
$ \Rightarrow \sin x(\cos x - 1) = 0$
A factor should be zero.
$ \Rightarrow \sin x = 0$ or $\cos x - 1 = 0$
$ \Rightarrow \sin x = 0$ or $\cos x = 1$
We know, the general solution of $\sin x = 0$ is $x = n\pi $
and for $\cos x = 1$
We know, $\cos {0^ \circ } = 1$
So, $\cos x = \cos {0^ \circ }$
$ \Rightarrow \cos x = \cos \alpha $
$ \Rightarrow x = 2n\pi \pm \alpha $
Here, $\alpha = {0^ \circ }$
So, $x = 2n\pi \pm 0$
$ \Rightarrow x = 2n\pi $
Thus, $x = n\pi $ or $x = 2n\pi $ , where $n \in Z$ and n is integer.
Additional information:
You can also solve this by taking $\tan x$ to the right-hand side.
$ \Rightarrow \sin x = \tan x$
$ \Rightarrow \sin x = \dfrac{{\sin x}}{{\cos x}}$
$ \Rightarrow \sin x\cos x = \sin x$
Bring $\sin x$ to the left-hand side,
$ \Rightarrow \sin x\cos x - \sin x = 0$
Take $\sin x$ common
$ \Rightarrow \sin x(\cos x - 1) = 0$
Factors should be zero
$ \Rightarrow \sin x = 0$ or $\cos x - 1 = 0$
$ \Rightarrow \sin x = 0$ or $\cos x = 1$
We know, $\cos {0^ \circ } = 1$
So, $\cos x = \cos {0^ \circ }$
$ \Rightarrow \cos x = \cos \alpha $
$ \Rightarrow x = 2n\pi \pm \alpha $
Here, $\alpha = {0^ \circ }$
So, $x = 2n\pi \pm 0$
$ \Rightarrow x = 2n\pi $
Thus, $x = n\pi $ or $x = 2n\pi $ $n \in Z$ and n is integer.
Note: The general solution of $\sin x = 0$ is $x = n\pi $ , general solution of $\cos x = 1$ is $x = 2n\pi $ , general solution of $\cos x = 0$ is $x = (2n + 1)\dfrac{\pi }{2}$ and general solution of $\tan x = 0$ is $x = n\pi $ where $n \in Z$ and n is integer.
Range of $\sin x = [ - 1,1]$ ,domain is all real numbers and period $ = 2\pi $
Range of $\cos x = [ - 1,1]$ ,domain is all real numbers and period $ = 2\pi $
Range of $\tan x = $ all real numbers, domain is $R - (2k + 1)\dfrac{\pi }{2}$ , $k \in Z$, k is integer and R is real number , period $ = \pi $
Always try to reduce the trigonometric equations in simpler functions like $\sin \theta $, $\cos \theta $ to make it easier to solve.
Always bring the right-hand side values to the left-hand side so as to factorize and make the factor zero for each.
Signs of all trigonometric functions should be taken care of for every interval or quadrant.
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