✔ 最佳答案
locus係要想盡辦法消去t
用配方法將t表為主項(不表也可以)
13.x=t^2-2t
=t^2-2t+1-1
=(t-1)^2-1
(x+1)^(1/2)+1=t
t^2=3-y
〔(x+1)^(1/2)+1〕^2=3-y
x+1+2(x+1)^(1/2)+1=3-y
2(x+1)^(1/2)=1-y-x
4(x+1)=y^2+x^2-2x-2y+1
y^2+x^2-6x-2y-3=0
14.t+1/t係一個特別組合,因為將佢2次,中間項係常數,再睇埋d係數,
(3x)^2-(2y)^2=36t^2+72+36/(t^2)-36t^2+72-36/(t^2)=144
9x^2-4y^2-144=0
15.t^2=x+1,t^4=y-1
(x+1)^2=y-1
y=x^2+2x+2
16.若將x,y兩邊2次,然後x^2+y^2,可以costsint項約走,即
x^2=4(cost)^2+4costsint+(sint)^2
y^2=(cost)^2-4costsint+4(sint)^2
x^2+y^2=5(cost)^2+5(sint)^2=5
17.設M(x,y)
x=(0+2t)/2,x=t
y=(t^2-2)/2
y=(x^2-2)/2=(1/2)x^2-1
18.設M(x,y)
x=(2cosθ+4)/2
=cosθ+2
x-2=cosθ
y=(2sinθ+0)/2
=sinθ
(x-2)^2+(y)^2=(cosθ)^2+(sinθ)^2=1