高数:已知点A(1,-1,2) B(5,-6,2) C(1,3,-1)答:AB:(4,-5,0)AC:(0,4,-3)同时与向量AB,AC垂直的向量 AB X AC = i j k 4 -5 0 0 4 -3 =15i+12j+16k 单位向量为:3/5i+12/25j+16/25k 面积为:1/2*|AB X AC|=25/2
大一高数题,求过程解答。图形面积。旋转体体积,答:y' = 2x; A(1, 1)处, x = 1, k = 2, k' = -1/k = -1/2法线: y - 1 = (-1/2)(x - 1), y = -x/2 + 3/2, 与x轴交于B(3, 0)绕y轴旋转, 用y做自变量比较容易, 积分区间是[0, 1], 在该区间内, 旋转体为圆环, 内径为r = x = √y; 外径R = x = ...