Question

已知|a|=√3,|b|=2.a与b夹角为30°,求|a+b|、|a-b|.

Answer 1

|a+b|²=(a+b)²=a²+2ab+b²=|a|²+2|a||b|cos30°+|b|²=13|a+b|=√13|a-b|²=(a-b)²=a²-2ab+b²=|a|²-2|a||b|cos30°+|b|²=1|a-b|=1