已知抛物线C的顶点在原点,焦点在x轴上,且抛物线上有一点P(4,m)到焦点的距离为7

1.抛物线上有一点P(4,m),4 > 0,顶点在原点,焦点在x轴上,y² = 2px
P(4,m)到焦点的距离为7 = p/2
p = 14
y² = 28x
2.(kx - 2)y² - 28x = 0
k²x² -4(k +7)x + 4 = 0
x₁ + x₂ = 4(k + 7) = 2*1
k = -13/2第一问就求错了对不起，把P当顶点了。7² = (4 - p/2)² + m² = 16 - 4p + p²/4 + 2p*4 = (4 + p/2)²p/2 + 4 = 7p = 6y² = 12xk²x² -4(k +3)x + 4 = 0x₁ + x₂ = 4(k + 3)/k² = 2*1k² - 2k - 6 = 0k = 1± √7∆ = 48(2k + 3) > 0k > -3/2, 舍去1-√7 < -3/2