Question

If A and B are supplementary, then find the value of cos A cos B - sin A sin B.
A)1
C)O
D)-1
B)2
MAARVAN​

Answer 1

Answer:

-1

A+B =180(Given)

then, B=180-A

Now,

cosA cos(180-A) - sinA sin (180-A)    ............equ.1

Rule of trigonometry-

cos(180-a)= -cosa  

sin(180-a)= sina    

thus, In eq.

-cos squareA -sinsquareA

-(cossquareA+sinsquareA)               (cossquareA+sinsquareA)=1 (rule of trig..)

= -1

other method-

cosa cosb -sina sinb =cos(a+b)

cos(180)= -1

Step-by-step explanation: