Question

How cos^2 a - sin^2 a = 2cos a ?​

Answer 1

Step-by-step explanation:

Let us first find the value of left hand side (LHS) that is cos

2

A−sin

2

A as shown below:

cos

2

A−sin

2

A

=cos

2

A−(1−cos

2

A)(∵1−cos

2

x=sin

2

x)

=cos

2

A−1+cos

2

A

=2cos

2

A−1=RHS

Since LHS=RHS,

Hence, cos

2

A−sin

2

A=2cos

2

A−1.