12. 已 知
【用戶】Liou
【年級】國二下
【評論內容】設v(x,y)x2+y2=20(x+1)2+(y+2)2=252x+4y=0x=-2yx=4、y=-20.5*|u|X|v| [外積] = 0.5*|1*y-2*x|=0.5*10=5