26 北一女中數學講義——高三數學總複習
y=3x
(-1,²)
(2)在坐標平面上, 設 A(1,-2),B(0,-1)及L:3x-y=0, 點P在L上,
求PA+PB的最小值及此時P點坐標
ABBAL
3-²)
0-(
>> A, B
B.10.-19
(1₁-2)
1 7 B 7 e 9 > 3 x ≤ 6 9 1 23826
(746) A' (acb)
a +36=5
3a-b=-5
-394-36=-15
A
G = | H
b=2
P
L
PATIB = A'B P√ 4²
13mg=1 ti
ptf
y=3x
X²
=)
hyosai gea
4y= = x-₁² y = =/ AB = y=-3x -1 2²3 2²4 ²²
1d +