more about factorization[help]

👨🏻‍🏫 學術台數學

用戶136249

2009-07-20 6:48 pm

factorize the following expressions:

x^2 - y^2 + 4x + 8y -12

can someone give me the steps to solve this expressions?
I've tried this many times......
i'sick of this

Oh, i have something to ask too,
about percentage,
my book teaches about salary tax,
Do I need to memorize all the 'salary tax allowance' or 'salaries tax rate'?

someone plz help me.......

更新1:

i know the ans is ( x + y - 2) ( x - y + 6) but i don't understand how to get this ans

更新2:

re: 002 ans = x^2 + 4x - (y - 2)(y - 6) = x^2 + [(y - 2) - (y - 6)]x - (y - 2)( y - 6) 4x = [ (y-2) - (y-6)]x ????

回答 (4)

用戶9112

2009-07-20 7:56 pm

✔ 最佳答案

x^2 - y^2 + 4x + 8y -12
= x^2 + 4x - (y^2 - 8y + 12)
= x^2 + 4x - (y - 2)(y - 6)
= x^2 + [(y - 2) - (y - 6)]x - (y - 2)( y - 6)
= [x - (y - 6)][x + (y - 2)]
=(x - y + 6)(x + y -2)
No need to memorise the tax rate and allowance.

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cipker

2009-07-23 12:24 am

You do not need to memorise the tax rate and allowance as it will varies.
But it is VERY IMPORTANT to know the method to calculate the salary tax because it may appears in your exam paper(even open exam)!!!

2009-07-22 16:25:02 補充：
Interest rate(simple and compound interest) problem(it should be in your text book) may also appears in your exam paper!!!

You should memorise the method to calculate the salary tax and interest.

Many people forget this after they finish form 3.

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ricky

2009-07-20 9:42 pm

x^2-y^2+4x+8y-12
=x^2+4x+4-(y^2-8y+16)
=(x+2)^2-(y-4)^2
=(x+2+y-4)(x+2-y+4)
=(x+y-2)(x-y+6)

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Ivan

2009-07-20 7:02 pm

x^2 - y^2 + 4x + 8y - 12
= x^2 + 4x – 5 – y^2 + 8y – 7
= x^2 + 4x – 5 – (y^2 – 8y + 7)
= (x – 1)(x + 5) – (y –1)(y-7)

if you are studying maths only
no need to memorize the 'salary tax allowance' or 'salaries tax rate'.

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