A middle school exam in the third grade of mathematics is online and so on.

According to the image, a (4,0) b (1,0) c (0,3).

Substitute parabola y=-3/4x? In +mx+n, we can get {- 12-4m+n = 0 ① n =-3 ②.

∴m= 15/4 n=-3, and the analytical formula of∴ parabola is y=-3/4x? + 15/4x-3

Substituting a (4,0) into y=kx-3, you can get y=3/4x-3.

Let D(x, -3/4x? +15/4x-3), and the parallel lines with D as the Y axis intersect with AC and E,

∴E(x,3/4x-3),∴DE=-3/4x？ + 15/4x-3-(3/4x-3)=-3/4x？ +3 times

When x=-b/2a=-3/(-4/3)×2=2, then y =-3/2.

There is a point D(2, -3/2) on the parabola above the straight line CA, which makes the area of △ACD the largest.

You can ask if you don't understand, thank you! !