consider two lines L1 : x+2y-7=0 and L2: 2x-y-9=0
(a)find the coordinates of the point of intersection of L1 and L2 .
(b)find the equation of the circle passing through the point of intersection of the above two lines,(-2,0) and (6,0)
點解AND 點做
maths f5
2011-12-18 1:44 am
回答 (2)
2011-12-18 2:17 am
✔ 最佳答案
(a) L1 : x+2y-7=0 and L2: 2x-y-9=0Solve it, y = 2x + 9, x + 2(2x - 9) - 7 = 0
x = 5, y = 1 intersection point (5,1)
(b) Let the equation of circle: x^2 + y^2 + Dx + Ey + F = 0
Sub. three points,
26 + 5D + E + F = 0
4 - 2D + F = 0
36 + 6D + F = 0
Solve it,
D = -10, E = 48, F = -24
The equation of circle x^2 + y^2 - 10x + 48y - 24 = 0
2011-12-18 8:48 am
點做知識長講左
我講點解
(a) 找L1L2相交點坐標
(b) 搵圓方程, 其中佢穿過個相交點同埋(-2,0), (6,0)
2011-12-18 00:59:23 補充：
solve it 個到教埋你
26 + 5D + E + F = 0 ...(1)
4 - 2D + F = 0 ...(2)
36 + 6D + F = 0 ...(3)
你見到(1)多左個E, (2),(3)都係得2個VAR.
你可以SOLVE左(2),(3)先
(3)-(2)就消左個F先, 32+8D=0 => D= - 4
SUB番入去(2)或(3)就搵到F
F=2D-4= - 12
最後SUB番去(1), 就有埋 E=-26-5D-F=6
D= -4, E=6, F= -12
(知識長計錯左)
我講點解
(a) 找L1L2相交點坐標
(b) 搵圓方程, 其中佢穿過個相交點同埋(-2,0), (6,0)
2011-12-18 00:59:23 補充：
solve it 個到教埋你
26 + 5D + E + F = 0 ...(1)
4 - 2D + F = 0 ...(2)
36 + 6D + F = 0 ...(3)
你見到(1)多左個E, (2),(3)都係得2個VAR.
你可以SOLVE左(2),(3)先
(3)-(2)就消左個F先, 32+8D=0 => D= - 4
SUB番入去(2)或(3)就搵到F
F=2D-4= - 12
最後SUB番去(1), 就有埋 E=-26-5D-F=6
D= -4, E=6, F= -12
(知識長計錯左)
收錄日期: 2021-04-23 20:47:12
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20111217000051KK00660