# 英文數學工課一頁,急要數學高手幫忙,急要答案

(要求有步驟)

Rating

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

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

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

• Anonymous
6 years ago

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些俊亙咇単

• 6 years ago

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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