∵ 丨a丨= 丨b丨= 1 ,cos θ = 60°
∴ (a - b)(a + 2 b)
= a ² + a · b - 2 b ²
= 丨a丨² + 丨a丨丨b丨cos θ + 2 × 丨b丨²
= 1 ² + 1 × 1 × cos 60° + 2 × 1 ²
= 1 + 1 / 2 + 2
= 7 / 2
∵ 丨a丨= 丨b丨= 1 ,cos θ = 60°
∴ (a - b)(a + 2 b)
= a ² + a · b - 2 b ²
= 丨a丨² + 丨a丨丨b丨cos θ + 2 × 丨b丨²
= 1 ² + 1 × 1 × cos 60° + 2 × 1 ²
= 1 + 1 / 2 + 2
= 7 / 2