Question

已知平面直角坐标系中,点O为原点,A(-3,-4),B(5,-12),求OA*OB?

Answer 1

O(0,0),A(-3,-4),B(5,-12),

OA^2=(0+3)^2+(0+4)^2=25,OA=5;

OB^2=(0-5)^2+(0+12)^2=169,OB=13;

OA*OB=5*13=65.