Expand the followig expressions.
1) (m-4n)(4n-m)
2) [(2x+y)+3][(2x+y)-3]
F.2 MATHZ QUICK PLZ HELP
2007-11-06 6:22 am
回答 (6)
2007-11-06 6:30 am
✔ 最佳答案
1) (m-4n)(4n-m)=-(m-4n)(m-4n)
= -(m-4n)^2
= -[m^2 - 4(m)(4n) + (4n)^2]
= -(m^2 - 16mn + 16n^2)
= 16mn - m^2 - 16n^2
2) [(2x+y)+3][(2x+y)-3]
= (2x+y)^2 - 3^2
= [(2x)^2 + 2(2x)(y) + y^2] - 9
= 4x^2 + 4xy + y^2 - 9
2007-11-07 4:21 am
(M-4n)(4n-M)
=4N(m-4n)-m(M-4n)
=4mn-16n^2-M^2+4mn
=8mn-16n^2-M^2
[(2x+y)+3][(2x+y)-3]
=(2x+y)^2-3^2
=4X^2+4XY+y^2-9
2007-11-06 20:23:58 補充：
[(2x y) 3][(2x y)-3]=(2x y)^2-3^2 --------use formula (a b)(a-b)=a^2-b^2=4X^2 4XY y^2-9
=4N(m-4n)-m(M-4n)
=4mn-16n^2-M^2+4mn
=8mn-16n^2-M^2
[(2x+y)+3][(2x+y)-3]
=(2x+y)^2-3^2
=4X^2+4XY+y^2-9
2007-11-06 20:23:58 補充：
[(2x y) 3][(2x y)-3]=(2x y)^2-3^2 --------use formula (a b)(a-b)=a^2-b^2=4X^2 4XY y^2-9
參考: me
2007-11-07 2:33 am
(Perfect Square)
1) (m-4n)(4n-m)
= -(m-4n)(m-4n)
= -(m-4n)^2
=-[m^2-2(m)(4n)+(4n)^2]
=-[m^2-8mn+16n^2]
=-m^2+8mn-16n^2
(Different of 2 squares & perfect square)
2) [(2x+y)+3][(2x+y)-3]
=(2x+y)^2-3^2
=[(2x)^2+2(2x)(y)+y^2]-9
=(4x^2+4xy-y^2)-9
=4x^2+4xy-y^2-9
1) (m-4n)(4n-m)
= -(m-4n)(m-4n)
= -(m-4n)^2
=-[m^2-2(m)(4n)+(4n)^2]
=-[m^2-8mn+16n^2]
=-m^2+8mn-16n^2
(Different of 2 squares & perfect square)
2) [(2x+y)+3][(2x+y)-3]
=(2x+y)^2-3^2
=[(2x)^2+2(2x)(y)+y^2]-9
=(4x^2+4xy-y^2)-9
=4x^2+4xy-y^2-9
參考: me
2007-11-06 10:14 am
1) (m-4n) (4n-m)
= 4mn - m^2 - 16n^2 + 4mn
= -(m^2 - 16n^2)
= -(m^2 - (4n)^2)
= -(m + 4n) (m - 4n)
2) [(2x + y) + 3] [(2x + y) - 3]
= (2x + y)^2 - 3^2
= 4x^2 + 4xy + y^2) - 9
= 4mn - m^2 - 16n^2 + 4mn
= -(m^2 - 16n^2)
= -(m^2 - (4n)^2)
= -(m + 4n) (m - 4n)
2) [(2x + y) + 3] [(2x + y) - 3]
= (2x + y)^2 - 3^2
= 4x^2 + 4xy + y^2) - 9
2007-11-06 7:00 am
1) (m-4n)(4n-m)
= 4mn-m^2-16n^2+4mn
= -(m^2-16n^2)
= -(m^2-(4n)^2)
= -(m+4n)(m-4n)
2) [(2x+y)+3][(2x+y)-3]
= (2x+y)^2-3^2
= (4x^2+4xy+y^2)-9
2007-11-05 23:02:25 補充：
1) 打錯1) (m-4n)(4n-m)= 4mn-m^2-16n^2 4mn= -(m^2-16n^2)= -(m^2-(4n)^2)= 4n^2-m^2
= 4mn-m^2-16n^2+4mn
= -(m^2-16n^2)
= -(m^2-(4n)^2)
= -(m+4n)(m-4n)
2) [(2x+y)+3][(2x+y)-3]
= (2x+y)^2-3^2
= (4x^2+4xy+y^2)-9
2007-11-05 23:02:25 補充：
1) 打錯1) (m-4n)(4n-m)= 4mn-m^2-16n^2 4mn= -(m^2-16n^2)= -(m^2-(4n)^2)= 4n^2-m^2
參考: 自己
2007-11-06 6:32 am
1) (m-4n)(4n-m)
= 4mn - 16n² - m² - 4mn
= -(m² + 16n²)
........................................
2) [(2x+y)+3][(2x+y)-3]
let (2x + y) be a
then [(2x+y)+3][(2x+y)-3]
= [a + 3] [a - 3]
=a² - 9
= (2x + y)² -9
=4x² + 4xy + y² - 9
= 4mn - 16n² - m² - 4mn
= -(m² + 16n²)
........................................
2) [(2x+y)+3][(2x+y)-3]
let (2x + y) be a
then [(2x+y)+3][(2x+y)-3]
= [a + 3] [a - 3]
=a² - 9
= (2x + y)² -9
=4x² + 4xy + y² - 9
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