x+y=0.2,x+3y=1
相加
2x+4y=1.2
x+2y=0.6
3x^2+12xy+12y^2
=3(x^2+4xy+4y^2)
=3(x+2y)^2
=3*0.6^2
=1.08
（1） (x^2-6x+9)/(x^2-4)
=(x-3)^2/(x-2)(x+2)
寫錯了,如果是(x^2-6x+9)/(x^2-9)則
=(x-3)^2/(x+3)(x-3)
=(x-3)/(x+3)
（2） (x^2-4x)/(x^2-8x+16)
=x(x-4)/(x-4)^2
=x/(x-4)
(1) 1/(x-4)=4/(x^2-16)
1/(x-4)=4/(x+4)(x-4)
兩邊乘(x+4)(x-4)
x+4=4
x=0
經(jīng)檢驗,x=0是方程的解
(2) 3/(x-1)-(x+2)/[x(x-1)]=0
兩邊乘x(x-1)
3x-(x+2)=0
2x-2=0
x=1
經(jīng)檢驗,x=1使公分母x(x-1)=0,是增根,舍去
所以方程無解
(3) (2-x)/(x-3)+1/(3-x)=1
(2-x)/(x-3)-1/(x-3)=1
兩邊乘x-3
2-x-1=x-3
2x=4
x=2
經(jīng)檢驗,x=2是方程的解