Question

Is the following statement true? Explain.

" For any two angles A and B, cos (A+B)=cos (A)+cos (B) "

Answer 1

Explanation:

We can prove the statement is false by proof of contradiction:

We know that cos0° = 1 and cos90° = 0.

Let A = 0° and B = 90°.

Left-Hand Side:

cos(A + B) = cos(0° + 90°) = cos90° = 0.

Right-Hand Side:

cos(A) + cos(B) = cos(0°) + cos(90°)

= 1 + 0 = 1.

Since LHS =/= RHS, by proof of contradiction,

the statement is false.