tolong bantu diselesaikan kak beserta caranya

Materi : Vektor
Kelas : X SMA

Ia + bI = V13 => Ia + bI^2 = 13
IaI = 4V3 => IaI^2 = 16.3 = 48
IbI = 5 => IbI = 25

Ia + bI^2 = IaI^2 + IbI^2 + 2IaIIbI cos a
13 = 48 + 25 + 2(4V3)(5) cos a
13 = 73 + 40V3 cos a
13 - 73 = 40V3 cos a
-60 = 40V3 cos a
-60/40V3 = cos a
(-60/40V3) × (40V3 / 40V3) = cos a
-2400V3 / 1600.3 = cos a
-4/3 V3 = cos a

Vektor
Pembahasan terlampir

Syarat menguasai vektor:
- pahami aturan cosinus
- ingat sudut-sudut istimewa beserta tanda +/- di setiap kuadran
- pahami proyeksi vektor