Question

Can someone pls help? ab to fail geometry. any help is nice.

Answer 1

By the law of cosines, the angle $C$ satisfies

$8.77^2=2^2+9^2-2\times2\times9\times\cos C$

which reduces to

$\cos C=0.2246\implies C=\arccos(0.2246)\approx1.34422\text{ rad}$

which converts to approximately 77 degrees (this can be done my multiplying by 180 and dividing by pi).