Question

if cos (A+B ) = cosA. cosB - sinA.sinA then find the value of cos 105​

Answer 1

Answer:

1-√3/2√2

Step-by-step explanation:

cos(105°)=cos(60°+45°)

By using the formula cos(A+B)=cosA.coosB-sinA.sinB, we get

cos(60°+45°)=cos 60°.cos 45°-sin 60.sin 45° = =(1/2). (1/√2)-(√3/2). (1/√2)

(by multiplying )

=1-√3/2√2

therefore cos(105°)=1-√3/2√2