Question

it is right to say that cos(A+B)=cosA+cosB Justify your answer

Answer 1

here you go...............

Answer 2

No.
cos(A+B) ≠ cosA + cosB

PROOF :

• let A = 0° and B = 90°

now,
cos( A + B ) = cos( 0° + 90° )
= cos(90°)
• cos( A + B ) = 0_________(1)

again,
cosA + cosB = cos0° + cos90°
= 1 + 0
• cosA + cosB = 1_________(2)

from (1) & (2)

cos(A+B) ≠ cosA + cosB