在平面直角坐标系中已知向量a={cos(α-20°),sin(α-20°)},向量b={cos(α+40°),sin(α+40°)}则|a-b| =
问题描述:
在平面直角坐标系中已知向量a={cos(α-20°),sin(α-20°)},向量b={cos(α+40°),sin(α+40°)}则|a-b| =
答
|a-b|^2=[cos(α-20°)-cos(α+40°) ]^2 + [sin(α-20°)-sin(α+40°)]^2=[cos(α-20°)]^2+[cos(α+40°)]^2-2cos(α-20°)*cos(α+40°)+[sin(α-20°)]^2+[sin(α+40°)]^2-2sin(α-20°)*sin(α+40...