MATHS EASY,f.2(10)!!!

👨🏻‍🏫 學術台數學

[匿名]

2013-11-28 3:01 am

when should we use this identity_____b-a=(-1)(a-b)

why
----(-3r+2s)(3r+2s) cannot use???

why
(2x-1)y+2x-1)
can use???

chinese and eng (explain
)
thx!!

回答 (4)

小紫雲　星空副帳

2013-11-29 6:01 am

✔ 最佳答案

Proof :
(-3r+2s)(3r+2s)
=(2s+3r)(2s-3r)
=4s^2-9r^2

let a = -2s and b = -3r
(-3r+2s)=-(-2s+3r)
(-3r+2s)(3r+2s)
=-(-2s+3r)(3r+2s)
=-(9r^2-4s^2)
=4s^2-9r^2

Also
(2x-1)(y+2x-1)=2xy-y-(2x-1)(1-2x)
=2xy-y-(2x-4x^2-1+2x)
=2xy-y-4x+4x^2+1
=4x^2-4x-2xy+1

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少年時

2013-11-29 12:45 am

阿 Sir, 你真的明她在問甚麼嗎？
我跟 Kwok Sir 一樣，一點也不明！

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