正方ABCD-A1B1C1D1的棱長(zhǎng)為a,點(diǎn)M分向量AC1的比為1/2,N為BB1的中點(diǎn),則 向量MN的長(zhǎng)度為

熱心網(wǎng)友

三角形ANC1中，顯然：AC1 = (genhao3)a；AN=NC1=(genhao5)a/2；cos角NAC1 =(genhao15)/5三角形AMN中：AM=AC1/3 = (genhao3)a/3MN^2 = AM^2 + AN^2 - 2*AM*AN*cos角NAC1== MN = (genhao21)a/6

熱心網(wǎng)友

三角形ANC1中，顯然：AC1 = (genhao3)a；AN=NC1=(genhao5)a/2；cos角NAC1 =(genhao15)/5三角形AMN中：AM=AC1/3 = (genhao3)a/3MN^2 = AM^2 + AN^2 - 2*AM*AN*cos角NAC1== MN = (genhao21)a/6