∫B, d in ellipse x? /4+3y? /4= 1
∴{x 1? /4+3y 1? /4= 1①
x2? /4+3y2? /4= 1②
①-② Acquisition
(x 1-x2)(x 1+x2)/4=﹣3(y 1-y2)(y 1+y2)/4
(x 1-x2)(x 1+x2)=﹣3(y 1-y2)(y 1+y2)
﹣ 1/3 =(y 1-y2)(y 1+y2)/(x 1-x2)(x 1+x2)
That is kbd * kon =- 1/3.
Question KAC = Tan 135 =- 1
Let AC: y =-x+b
Ac intersection (1, 2)
∴AC:y=﹣x+3
Ac vertical BD
∴KBD= 1, which means kon = ∴ 1/3.
Because n is on ac
That is x0+y0-3 = 0.
yo/x0=﹣ 1/3
∴x0=9/2y0=﹣3/2
BD:y=x﹣6