Mohon bantuannya.. Dikumpulin hari ini.. Pertanyaanya diganti a dot b

Vektor

diketahui |a| = 3 ; |b| = 4
dan cos 120° = -1/2

rumus yang digunakan 
a . b = |a| |b| cos 120°
a . a = |a|²
====================================

>> a . (b + a)
= a . b + a . a
= |a| |b| cos 120° + a . a
= 3 . 4 . -1/2 + 3²
= -6 + 9
= 3

>> b . (a + b)
= b . a + b . b
= |b| |a| cos 120° + |b|²
= 4 . 3 . -1/2 + 16
= -6 + 16
= 10