The 1-cosx identity is given by 1-cosx= 2sin2(x/2). 1 minus cosx is a trigonometric expression and its formula is given below:
$1-\cos x =2 \sin^2 (\frac{x}{2})$.
Let us now find the formula of 1-cosx in terms of sin.
1-cosx Formula in Terms of Sin
Answer: 1-cosx formula in terms of sin is equal to 1-cosx= 2sin2(x/2).
Explanation:
The given expression is
1- cosx
= 1-cos $\big(2 \cdot \dfrac{x}{2} \big)$ as we can write x=2⋅x/2.
= $1- \big[\cos^2 \dfrac{x}{2} – \sin^2 \dfrac{x}{2} \big]$, obtained by using the formula: cos2A= cos2A -sin2A.
= $1- \cos^2 \dfrac{x}{2} + \sin^2 \dfrac{x}{2}$
= $\sin^2 \dfrac{x}{2} + \sin^2 \dfrac{x}{2}$, by the identity 1-cos2A=sin2A.
= $2\sin^2 \dfrac{x}{2}$
Therefore, $1-\cos x=2\sin^2 \dfrac{x}{2}$.
So the formula of 1-cosx in terms of sin is given by 1-cosx= 2sin2(x/2).
Also Read: Sin3x formula in terms of sinx
Cos3x formula in terms of cosx
Solved Examples
Example 1: Find the value of 1-cos120°.
Solution:
By the above formula,
1-cos120°
= 2sin2(120/2)°
= 2sin260°
= 2 × $(\frac{\sqrt{3}}{2})^2$ as the value of sin60 is √3/2.
= (2 ×3)/4
= 3/2.
So the value of 1-cos120° is equal to 3/2.
Read Also: cot(a+b)cot(a-b) Formula
FAQs
Q1: What is the formula of 1-cosx?
Answer: The formula of 1-cosx is given by 1-cosx= 2sin2(x/2).