maths

Prove (2x-3)/3-(3x-4)/4=-x/12
L.H.S.
=(2x-3)/3-(3x-4)/4
=[4(2x-3)-3(3x-4)]/12
=(8x-12-9x+12)/12
=-x/12=R.H.S.
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Prove (4h+5)/3-(7h+2)/9=5h+13/9 [I think you missed the 3]
L.H.S.
=(4h+5)/3-(7h+2)/9
=[3(4h+5)-(7h+2)]/9
=(12h+15-7h-2)/9
=(5h+13)/9=R.H.S.



2008-01-25 17:48:41 補充：
補充番先,如果係要決定條式係咪恆等式,咁第2題就唔係喇,因為要係13先得,1就唔係喇。(-2y-1/2x)(-1/2x+2y) =xy-4y^2+(x^2)/4-xy=(x^2)/4-4y^2(x+a)(x-a)(x^2+a^2) =(x^2-a^2)(x^2+a^2)-------[Using(a-b)(a+b)=(a^2-b^2)]=[(x^2)^2-(a^2)^2]=(x^4-a^4)

1)
Left Hand Side (LHS)
Right Hand Side = -x/12

LHS
= (2x-3/3) - (3x-4/4)
= (8x-12/12) - (9x-12/12)
= 8x-12-9x-(-12) / 12
= -x /12 = RHS

it is an identity
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LHS = 4h+5/3-7h+2/9
RHS = 5h+1/9

這樣看不清楚..
究竟 4h 是跟 5 一起做份子定係獨立一個數?
-7h 是跟 3 除還是獨立一個數字...

如果我當兩個都係跟在份數內... 不是 identity..

2x-3/3-3x-4/4=-x/12

L.H.S=8x-12/12-9x-12/12

=8x-12-9x-12/12

=-x/12

R.H.S=-x/12

2x-3/3-3x-4/4=-x/12 is an identity


4h+5/3-7h+2/9=5h+1/9

L.H.S=12h+15/9-7h+2/9

=12h+15-7h+2/9

=5h+17/9

R.H.S=5h+1/9

4h+5/3-7h+2/9=5h+1/9 is not an identity.

2008-01-25 17:40:03 補充：
2) You give me wrong so i don't do right.