Question

高一数学 3.

Answer 1

3、
a CD直线方程：(y-11)/(x-5)=(12-11)/(13-5)
(y-11)/(x-5)=1/8
8(y-11)=x-5
8y-88=x-5
x-8y+83=0
b kCD=1/8
AE⊥CD
kAE=-1/kCD
=-1/(1/8)
=-8
AE直线方程：y-17=-8(x-3)
y-17=-8x+24
8x+y-41=0
c BC直线方程：(y-11)/(x-5)=(20-11)/(7-5)
(y-11)/(x-5)=9/2
2(y-11)=9(x-5)
2y-22=9x-45
9x-2y-23=0
d x=8代入CD方程：x-8y+83=0
8-8y+83=0
-8y+91=0
-8y=-91
y=91/8
两街交点：(8,91/8)