Question

Cos (a+b)=cos a cos b -sin a sin b prove it vectorly

Answer 1

hi nice question !!
===============
See image first please!!
ok,
now
from image
Cos(A+B)= OM/OP
= ON/OP-MN/OP
= ON/OP-QR/OP
= ON/OQ×OQ/OP-QR/PQ×PQ/OP
=CosAcosB-sinAsinB

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>