yuxie123
幼苗
共回答了20个问题采纳率:100% 举报
(1) x = 2, y = -4(2 - m) = 2, m = 5/2
(2) B(-2, 0), C(5/2, 0)
x = 0, y = 5, E(0, 5)
S = (1/2)BC*E的纵坐标 = (1/2)(5/2 + 2)(5/2) = 45/8
(3) 对称轴x = (-2 + 5/2)/2 = 1/4
设过H(1/4, h)的水平线(与x轴平行)与BE交于D; 显然∠DHE = ∠DHB时, BH + EH最小
tan∠DHB = tan∠HBO = H的纵坐标/(H的横坐标 + 2) = h/(1/4 + 2) = 4h/9
tan∠DHE = (E的纵坐标 - D的纵坐标)/(H的横坐标 - E的横坐标) = (5 - h)/(1/4 - 0) = 4(5 - h)
4h/9 = 4(5 - h)
h = 9/2
H(1/4, 9/2)
(4)
tan∠CBE = 5/2, ∠CBE ≈ 68˚
tan∠BCE = 2, ∠CBE ≈ 63˚
∠BEC ≈ 49˚
三者均为锐角
在第四象限内,抛物线C1上点F使∠BCF > 90˚, F不存在
1年前
10