A-maths!!!

2007-06-03 8:26 am
已知兩直線L1:x+y+1=0和L2:7x-y+2=0。若d1和d2分別為從P點到L1和L2的垂直距離,求滿足下列條件時P點我軌跡方程:
(a)d1=d2
(b)d1=2d2

回答 (1)

2007-06-03 8:35 am
✔ 最佳答案
Let (x,y) be the coordinates of point P.

d1
= ⊥ distance from point P to L1
= │(x + y + 1)/√[(1)² + (1)²]│
= │(x + y + 1)/√2│

d2
= ⊥ distance from point P to L2
= │(x - y + 2)/√[(1)² + (-1)²]│
= │(x - y + 2)/√2│


a. Since d1 = d2

∴│(x + y + 1)/√2│=│(x - y + 2)/√2│
(x + y + 1) = (x - y + 2) or (x + y + 1) = -(x - y + 2)
2y = 1 or 2x = -3
y = 1/2 or x = -3/2

The equation of locus of point P are:
y = 1/2 or x = -3/2



b. Since d1 = 2d2

∴│(x + y + 1)/√2│=2│(x - y + 2)/√2│
(x + y + 1) = 2(x - y + 2) or (x + y + 1) = -2(x - y + 2)
x - 3y + 3 = 0 or 3x - y + 5 = 0

The equation of locus of point P are:
x - 3y + 3 = 0 or 3x - y + 5 = 0
參考: Myself~~~


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