Answers>Maths>A Level>Article

Using the identity cos(A+B)= cosAcosB-sinAsinB, prove that cos2A=1-2sin^2A.

Use cos(A+B)=cosAcosB-sinAsinB and let A=B so cos(A+A)=cosAcosA-sinAsinA this means cos(2A)=cos²A-sin²A and since cos²A+sin²A=1, cos²A=1-sin²A. Therefore, by subbing cos²A=1-sin²A into cos(2A)=cos²A-sin²A, we get cos(2A)=1-sin²A-sin²A=1-2sin²A.

Answered by Rebecca F. • Maths tutor

20483 Views

See similar Maths A Level tutors

Using the identity cos(A+B)= cosAcosB-sinAsinB, prove that cos2A=1-2sin^2A.

Related Maths A Level answers

Where do the kinematics equations (SUVAT) come from?

The line y = (a^2)x and the curve y = x(b − x)^2, where 0<a<b , intersect at the origin O and at points P and Q. Find the coordinates of P and Q, where P<Q, and sketch the line and the curve on the same axes. Find the tangent at the point P.

Find the integral between 4 and 1 of x^(3/2)-1 with respect to x

Differentiate with respect to x, x^2*e^(tan(x))

We're here to help

Company Information

Popular Requests

© MyTutorWeb Ltd 2013–2025

CLICK CEOP