Question

已知单位向量ab的夹角为60度,那么Ia+2bI（就是a+2b的绝对值）等于多少?

Answer 1

|a+2b|²

=(a+2b)²

=a²+4ab+4b²

=|a|²+4*|a|*|b|*cos(a^b)+4|b|²

=1+4*1*1*cos60+4

=5+2

=7

|a+2b|=根号7