Question

cos(a+b).cos(a-b) =?​

Answer 1

Answer:

cos(a+b)*cos(a-b) = cos^2a - sin^2b tan(x/2) = (1-cosx)/(sinx)

please click the brainliest answer .

Answer 2

Answer:

$\cos(A+B)\cdot\cos(A-B)=\cos^2A-\sin^2B=\cos^2B-\sin^2A$

Step-by-step explanation:

$\cos(A+B)\cdot\cos(A-B)=(\cos A\cdot\cos B-\sin A \cdot \sin B)(\cos A\cdot\cos B+\sin A \cdot \sin B)$

$=\cos^2 A\cdot \cos^2B - \sin^2 A \cdot \sin^2 B$

$=\cos^2 A \cdot (1-\sin^2 A)-(1-\cos^2 A)\cdot \sin^2 B$

$=\cos^2 A - \cos^2 A \cdot \sin^2 B - \sin^2 B + \cos^2 A \cdot \sin^2 B$

$=\cos^2A-\sin^2B$

Note that $\cos(A-B)=\cos(B-A)$

So, $\cos(A+B)\cdot\cos(A-B)=\cos^2B-\sin^2A$ is also true