Question

if cos(A+B)=cosAcosB-sinAsinB find the value of cos 105 degrees

Answer 1

we can consider A=60° and B=45°
thus cos(60+45)=1/2×1/2^(1/2)-3^(1/2)/2×1/2^(1/2)=(1-3^(1/2))/2×2^(1/2)
=-0.732/(2×1.414)
=-0.2588

Answer 2

Answer:

Step-by-step explanation:

Its easy

cos(60+45)=1/2×1/2^(1/2)-3^(1/2)/2×1/2^(1/2)=(1-3^(1/2))/2×2^(1/2)

=-0.732/(2×1.414)

=-0.2588