英文數學工課一頁,急要數學高手幫忙,急要答案

1.
x(3x+1)=0
x=0 or 3x+1=0
x=0 or 3x= -1
x=0 or x= -1/3

2.
x^2 - 4x=0
x(x-4)=0
x=0 or x-4=0
x=0 or x=4

3.
x^2 -8x+12=0

if you use quadratic formula︰
x^2 -8x+12=0
x=[-b+√(b^2-4ac)]/(2a) or [-b-√(b^2-4ac)]/(2a)
x={ -(-8) + √[(-8)^2-4(1)(12)] }/[2(1)] or x={ -(-8) - √[(-8)^2-4(1)(12)] }/[2(1)]
x=6 or x=2

if you use cross method︰
x^2 -8x+12=0

x -6
x -2
________
=-6x-2x=8x
∴(x-2)(x-6)=0
x=6 or x=2

if you use completing the square︰
x^2 -8x+12=0
x^2 -8x= -12
x^2 -8x +(8/2)^2 -(8/2)^2= -12
(x-4)^2 = -12+16
(x-4)^2 = 4
(x-4)= √4 or -√4
x=2+4 or -2+4
x=6 or 2

4. x^2 -8x+16=0


if you use quadratic formula︰
x^2 -8x+16=0
x=[-b+√(b^2-4ac)]/(2a) or [-b-√(b^2-4ac)]/(2a)
x={ -(-8) + √[(-8)^2-4(1)(16)] }/[2(1)] or x={ -(-8) - √[(-8)^2-4(1)(16)] }/[2(1)]
x=4

if you use cross method︰
x^2 -8x+16=0

x -4
x -4
________
=-4x-4x=8x
∴(x-4)(x-4)=0
x=4

if you use completing the square︰
x^2 -8x+16=0
x^2 -8x= -16
x^2 -8x +(8/2)^2 -(8/2)^2= -16
(x-4)^2 = -16+16
(x-4)^2 = 0
(x-4)=0
x=4

2014-01-15 18:28:56 補充：
In 3's cross method,
it should be
x -6
+ x -2
________
=(-6x)+(-2x)= -8x
∴(x-2)(x-6)=0
x=6 or x=2

In 4's cross method,
it should be
x -4
+ x -4
________
=(-4x)+(-4x)= -8x
∴(x-4)(x-4)=0
x=4

這家不錯*****買幾次啦真的一樣
些俊亙咇単

我覺得　HK~ 　答得好好～

^__^ 所以我刪去答案並贊助～

大家努力！

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