Question

PLEASE answer fast and don't answer irrelevant answers.........................​

Answer 1

Answer:

Step-by-step explanation:

cosA - cosB + cosC

=2sin((A+B)/2)sin((B-A)/2) + 1 - 2cos²(C/2)

A+B+C =180°

=2sin(90-c/2)sin((B-A)/2) + 1 - 2cos²(C/2)

=2cos(c/2)sin((B-A)/2) + 1 - 2cos²(C/2)

=1+2cos(c/2) {sin((B-A)/2) - cos(C/2)}

=1+2cos(c/2) {sin((B-A)/2) - sin((A+B)/2)}

=1+2cos(c/2) {2sinB/2cosA/2}

=1+4cosA/2sinB/2cosC/2