Maths--quadratic equation

👨🏻‍🏫 學術台數學

snapper

2009-07-30 3:14 am

The root of the equation 2x^2-7x+4=0 are a and b
(a) Write down the values a+b and ab
(b) Find the quadraic equation whose roots are a+2 and b+2

更新1:

Sorry,ｂpart不太明,点解会用哩個方法,有无其他alternative method

更新2:

不明,煩請解釋

更新3:

any other alternative method to get part b answer

回答 (3)

用戶7639

2009-07-30 3:49 am

✔ 最佳答案

(a)
Sum of roots=a+b
=-(-7)/2
=7/2
Product of roots=ab
=4/2
=2
(b)
Sum of roots=(a+2)+(b+2)
=(a+b)+4
=(7/2)+4
=15/2
Product of roots=(a+2)(b+2)
=ab+2a+2b+4
=ab+2(a+b)+4
=(2)+2(7/2)+4
=2+7+4
=13
The quadraic equation is:
x2-(15/2)x+13=0
2x2-15x+26=0

2009-07-29 23:37:20 補充：
其他做法就是你求左個a同b係咩先,
之後個quadraic equation就是[x-(a+2)][x-( b+2)]=0

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六呎將軍

2009-07-30 7:19 am

超凡學生的 ans 已係最簡單的方法:
凡有了 sum of roots = s, product of roots = p 時, 條 quadratic equation 皆為 x^2 - sx + p = 0

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snapper

2009-07-30 4:18 am

any other alternative methods to get part b answer

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