Pertanyaan vektor kelas 10 kak,susah nih kak mohon bantuanya

(a+b).(a+b) = 49
a²+b²+2a.b = 49
5²+3²+2.5.3.cosθ = 49
34 + 30 cosθ = 49
30 cosθ = 15
cosθ = 15/30 = ½
θ = 60°