Question

初三数学 一元二次方程 用配方法写 （写详细过程）

1. 3x平方-9x+2=0
2. 6x平方-7x+1=0
3. 5x平方-18=9x
4. 4x-3x=52
4题. 4x平方-3x=52

Answer 1

a^2表示a的平方； =>表示推得，/表示除以。
1. 3x^2-9x+2=0, =>x^2-3x=-2/3, => x^2-3x+9/4=-2/3+9/4, =>(x-3/2)^2=19/12, =>x-3/2=±√(19/12),
=> x=3/2±√(19/12);
2. 6x^2-7x+1=0, =>x^2-7x/6=-1/6 ,=>x^2-7x/6+49/144=-1/6+49/144, =>x=7/12±√(25/144)=7/12±5/12=1或1/6;
3. 5x^2-9x-18=0,=>x^2-9x/5+81/100=18/5+81/100,=>(x-9/10)^2=441/100,=>x=9/10±21/10;
4. 4x^2-3x=52,=>x^2-3/4x+9/64=13+9/64,=>(x-3/8)^2=841/64,=>x=3/8±29/8

Answer 2

1. 3x^2-9x+2=0, =>x^2-3x=-2/3, => x^2-3x+9/4=-2/3+9/4, =>(x-3/2)^2=19/12, =>x-3/2=±√(19/12),
=> x=3/2±√(19/12);
2. 6x^2-7x+1=0, =>x^2-7x/6=-1/6 ,=>x^2-7x/6+49/144=-1/6+49/144, =>x=7/12±√(25/144)=7/12±5/12=1或1/6;
3. 5x^2-9x-18=0,=>x^2-9x/5+81/100=18/5+81/100,=>(x-9/10)^2=441/100,=>x=9/10±21/10;
4. 4x^2-3x=52,=>x^2-3/4x+9/64=13+9/64,=>(x-3/8)^2=841/64,=>x=3/8±29/8