Question

已知向量a,向量b满足丨a丨=3,丨b丨=2丨a+b丨=4则丨a-b丨=

Answer 1

|a-b|^2=|a+b|^2-4a*b

|a+b|^2=a^2+2ab+b^2=16

9+2ab+4=16

2ab=3

|a-b|^2=|a+b|^2-4ab=16-2*3=10

|a-b|=根号10