gmn caranya guys... tolong bantuannya

R = √A²+B²+2AB cosa
= √ 9² + 9² + 2.9.9 cos 60
= √ 81 + 81 + 162 . 1/2
= √ 162 + 81
= √243
=√ 81.3
= 9√3

semoga membantu