向量a的模=2,向量b的模=1,向量a-b的模=根号3求向量a+b的模

Question

向量a的模=2,向量b的模=1,向量a-b的模=根号3 求向量a+b的模

Answer 1

3
=|a-b|²
=|a|²+|b|²-2|a||b|
=2²+1²-2|a||b|
=>|a||b|=1
|a+b|²
=|a|²+|b|²+2|a||b|
=7
|a+b|=√7