中二簡單數學~~~

1.-(m+3n)(m-3n)
=-[(m+3n)(m)(m+3n)(-3n)
=-[m^2+3nm-3mn-9n^2]
=-m^2-9n^2

2.-4(a-5b)(-5b-a)
=(-4a+20b)(-5b-a)
=[(-4a+20b)(-5b)(-4a+20b)(-a)]
=[20ab-100b^+4a^2-20ba]
= -100b^2+4a^2
Hope can help you
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2009-09-18 17:59:32 補充：
2.-4(a-5b)(-5b-a)



=(-4a+20b)(-5b-a)



=[(-4a+20b)(-5b)(-4a+20b)(-a)]



=[20ab-100b^2+4a^2-20ba]



= -100b^2+4a^2

1.-(m+3n)(m-3n)
= - (m^2 - 3mn + 3mn - 9n^2)
= - (m^2 - 9n^2)
= - m^2+9n^2

2.-4(a-5b)(-5b-a)
= - 4 ( a-5b) -1 (a+ 5b)
= 4 ( a-5b ) ( a+5b )
= 4 ( a^2 +5ab - 5ab - 25b^2 )
= 4 ( a^2 - 25b^2 )
= 4a^2 - 100b^ 2

1.
-(m+3n)(m-3n)
= -[m(m+3n)-3n(m+3n)]
= -(m^2+3mn-3mn-9n^2)
= -(m^2-9n^2)
= -m^2+9n^2
= 9n^2-m^2
2.
-4(a-5b)(-5b-a)
= -4[-5b(a-5b)-a(a-5b)]
= -4(-5ab+25b^2-a^2+5ab)
= -4(25b^2-a^2)
= -100b^2+4a^2
= 4a^2-100b^2
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