Math Doubts

Double angle identities

In trigonometry, there are four popular double angle trigonometric identities and they are used as formulae in theorems and in solving the problems. So, let’s learn each double angle identity with mathematical proof.

Sin Double angle identity

The sine of double angle is equal to two times the product of sine and cosine of angle.

$\sin{2\theta} \,=\, 2\sin{\theta}\cos{\theta}$

Cos Double angle identity

The cosine of double angle is equal to the subtraction of square of sine from square of cosine of angle.

$\cos{2\theta} \,=\, \cos^2{\theta}-\sin^2{\theta}$

Tan Double angle identity

$\tan{2\theta} \,=\, \dfrac{2\tan{\theta}}{1-\tan^2{\theta}}$

Cot Double angle identity

$\cot{2\theta} \,=\, \dfrac{\cot^2{\theta}-1}{2\cot{\theta}}$

Problems

Learn how to use the double angle trigonometric identities as formulae in mathematical problems.

Math Doubts
Math Doubts is a free math tutor for helping students to learn mathematics online from basics to advanced scientific level for teachers to improve their teaching skill and for researchers to share their research projects. Know more
Follow us on Social Media
Math Problems

Learn how to solve easy to difficult mathematics problems of all topics in various methods with step by step process and also maths questions for practising.

Learn more