Question

求解第二问 求过程 详细点

Answer 1

(1)

过A(1, 0), B(-3, 0), 可以表达为y = a(x - 1)(x +3)
x = 0, y = -3a = 3, a = -1
y = -x² - 2x +3

(2)
从D向x轴作垂线，垂直D'

D(d, -d² - 2d + 3), D'(d, 0)，C(0, 3), -3 < d < 0

四边形BOCD的面积 = 三角形BD‘D的面积 + 梯形D'OCD的面积
= (1/2)*BD'*D'D + (1/2)(D'D +OC)*D'O
= (1/2)(d + 3)(-d² - 2d + 3) + (1/2)(-d² - 2d + 3 + 3)*(-d)
= -(3/2)(d² + 3d -3)
= -(3/2)(d + 3/2)² + 63/6
最大值63/6, 此时d = -3/2, D(-3/2, 15/4)

(3)
对称轴x = (-3 + 1)/2 = -1
M(-1, m)
有三种可能：
(a) B为直角
BC的斜率为1, 则BM的斜率为 -1， 其方程为y = -(x + 3), 令x = -1, y = 2, M(-1, 2)

(b) C为直角
BC的斜率为1, 则CM的斜率为 -1， 其方程为y = -x + 3, 令x = -1, y = 4, M(-1, 4)

(c) M为直角
BM和CM的斜率分别为：
p = (m - 0)/(-1 + 3) = m/2
q = (m - 3)/(-1 - 0) = 3 - m
pq = m(3 - m)/2 = -1
m² - 3m - 2 = 0
m = (3 ± √17)/2

Answer 2

真难

追问

你会么 求你了555

比给采纳

追答

会也不答了，你这采纳不好得，费脑子和手