Question

If cosa=4/5,cosb=7/5 root2.prove that a+b=π/4

Answer 1

sina=root(1-cos^2a)=3/5
sinb=root(1-cos^2b)=1/5root2
cos(a+b)=cosa cosb -sinasinb=4/5×7/5root2-3/5×1/5root2=1/root2 =cos(45)=cos(pai/4) (proved)

Answer 2

Question:-

If $\cos \: = \frac{4}{5}$ $\cos = \frac{7}{ 5 \sqrt{2} }$

Prove that (A+B) =

$\frac{\pi}{4}$

Solution:-

Refer to the attachment