Question

已知向量a=(4,2),b=(1,3) （1）求a ,b的夹角 .（2）若（a+入b）⊥b,求入的值

Answer 1

(1)记原点为O,a的顶点为A,b的顶点为B,连接AB,有OB =（1 + 3^2)^(1/2) = 10^(1/2)AB =（(4-1)^2 + (3-2)^2)^(1/2) = 10^(1/2)OA = (4^2 + 2^2)^(1/2) = 20^(1/2)OB = AB 且 OB^2 + AB^2 = OA^2所以 △OAB是等腰直角三...