Tolong gan nomor berapa aja . harap jangan asal yah ^-^ pake cara gan . Makasih

18.
|a| = √2
|b| = 3
| a+b | = √5
|a+b|^2 = |a|^2 + |b|^2 +2|a||b|cos
5 = 2 + 9 + 2(3)√2 cos
6√2 cos teta = 5-11
6√2 cos teta = -6
cos teta = -√2/2
teta = 135°

semoga bermamfaat ::))