maka besar sudut antara a dan b adalah. . .

|a| = √6

(a - b)(a + b) = 0
|a|² + ab - ab - |b|² = 0
|a|² - |b|² = 0
|a|² = |b|²
(√6)² = |b|²
6 = |b|²
√6 = |b|

a(a - b) = 3
|a|² - a • b = 3
(√6)² - a • b = 3
6 - 3 = a • b
3 = a • b

a • b = |a| × |b| × cosA
3 = √6 × √6 × cosA
3 = 6 cosA
3/6 = cos A
1/2 = cos A
60° = A
π/3 = A (A)