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VH
2
HN
27 tháng 9 2017
\(a)37,5.8,5-7,5.3,4-6,6.7,5+1,5.37,5\)
\(=\left(37,5.8,5+1,5.37,5\right)-\left(7,5.3,4+6,6.7,5\right)\)
\(=37,5\left(8,5+1,5\right)-7,5\left(3,4+6,6\right)\)
\(=37,5.10-7,5.10\)
\(=10\left(37,5-7,5\right)\)
\(=10.30\)
\(=300\)
\(b)35^2+40^2-25^2+80.35\)
\(=\left(35^2+80.35+40^2\right)-25^2\)
\(=\left(35+40\right)^2-25^2\)
\(=75^2-25^2\)
\(=\left(75-25\right)\left(75+25\right)\)
\(=50.100\)
\(=5000.\)
PA
1
AN
27 tháng 9 2017
a)\(37,5\times8,5+-7,5\times3,4-6,6\times7,5+1,5\times37,5\)
\(=\left(37,5\times8,5+1,5\times37,5\right)-\left(7,5\times3,4+6,6\times7,5\right)\)
\(=37,5\left(8,5+1,5\right)-7,5\left(3,4+6,6\right)\)
\(=375-75\)
\(=300\)
ML
5
KN
28 tháng 9 2017
a) 37,5.8,5 - 7,5.3,4 - 6,6.7,5 + 1,5.37,5
= (37,5.8,5 + 1,5.37,5) - (7,5.3,4 + 6,6.7,5)
= 37,5(8,5 + 1,5) - 7,5(3,4 + 6,6)
=37,5.10 - 7,5.10
=375 - 75
= 300
b) 352 + 402 - 252 + 80.35
= (352 + 80.35 + 402) - 252
= (35 + 40)2 - 252
= (35 + 40 - 25)(35 + 40 + 25)
= 50.100
= 5000
M
0
5 tháng 10 2017
Bài 1:
a) \(x^2-y^2-2yz-z^2\)
\(=x^2-\left(y^2+2yz+z^2\right)\)
\(=x^2-\left(y+z\right)^2\)
\(=\left(x+y+z\right)\left(x-y-z\right)\)
b) \(2xy-x^2-y^2+16\)
\(=16-\left(x^2-2xy+y^2\right)\)
\(=4^2-\left(x-y\right)^2\)
\(=\left(4+x-y\right)\left(4-x+y\right)\)
c) \(3a^2-6ab+3b^2-12c^2\)
\(=3\left(a^2-2ab+b^2-4c^2\right)\)
\(=3\left[\left(a^2-2ab+b^2\right)-\left(2c\right)^2\right]\)
\(=3\left[\left(a-b\right)^2-\left(2c\right)^2\right]\)
\(=3\left(a-b-2c\right)\left(a-b+2c\right)\)
Bài 2:
a) \(37,5\cdot8,5-7,5\cdot3,4+6,6\cdot7,5+1,5\cdot37,5\)
\(=\left(37,5\cdot8,5+1,5\cdot37,5\right)-\left(7,5\cdot3,4-6,6\cdot7,5\right)\)
\(=37,5\cdot\left(8,5+1,5\right)-7,5\cdot\left(3,4-6,6\right)\)
\(=37,5\cdot10-7,5\cdot10\) (mk đoán đề bạn chép sai)
\(=10\cdot\left(37,5-7,5\right)\)
\(=10\cdot30\)
\(=300\)
b) \(35^2+40^2-25^2+80\cdot35\)
\(=\left(40^2+2\cdot40\cdot35+35^2\right)-25^2\)
\(=\left(40+35\right)^2-25^2\)
\(=75^2-25^2\)
\(=\left(75+25\right)\left(75-25\right)\)
\(=100\cdot50\)
\(=5000\)
DP
5 tháng 10 2017
Bài 1:
a, \(x^2-y^2-2yz-z^2=x^2-\left(y^2+2yz+z^2\right)\)
\(=x^2-\left(y+z\right)^2=\left(x-y-z\right)\left(x+y+z\right)\)
b, \(2xy-x^2-y^2+16=16-\left(x^2-2xy+y^2\right)\)
\(=16-\left(x-y\right)^2=\left(4-x+y\right)\left(4+x-y\right)\)
c, \(3a^2-6ab+3b^2-12c^2\)
\(=3\left(a-b\right)^2-12c^2=3\left[\left(a-b\right)^2-4c^2\right]\)
\(=3\left(a-b+2c\right)\left(a-b-2c\right)\)
Bài 2:
a, \(37,5.8,5-7,5.3,4+6,6.7,5+1,5.37,5\)
\(=37,5.\left(8,5+1,5\right)-7,5.\left(3,4+6,6\right)\)
\(=37,5.10-7,5.10=10.\left(37,5-7,5\right)\)
\(=10.30=300\)
b, \(35^2+40^2-25^2+80.35\)
\(=\left(40^2+2.40.35+35^2\right)-25^2\)
\(=\left(40+35\right)^2-25^2=75^2-25^2\)
\(=\left(75-25\right)\left(75+25\right)=50.100=5000\)
18 tháng 10 2017
\(37,5.8,5-7,5.3,4-6,6.7,5+1,5.37,5\)
\(=\left(37,5.8,5+1,5.37,5\right)-\left(7,5.3,4+6,6.7,5\right)\)
\(=37,5\left(8,5+1,5\right)-7,5\left(3,4+6,6\right)\)
\(=37,5.10-7,5.10\)
\(=10\left(37,5-7,5\right)\)
\(=10.30\)
\(=300\)
3 tháng 10 2017
\(37,5.8,5-7,5.3,4-6,6.7,5+1,5.37,5\)
\(=\left(37,5.8,5+1,5.3,5\right)+\left(-7,5.3,4-6,6.7,5\right)\)
\(=37,5\left(8,5+1,5\right)-7,5\left(3,4+6,6\right)\)
\(=37,5.10-7,5.10\)
\(=10.\left(37,5-7,5\right)\)
\(=10.30=300\)
27 tháng 9 2017
\(a,2x^2-2xt-5x+5y\)
\(=\left(2x^2-5x\right)-\left(2xy-5y\right)\)
\(=x\left(2x-5\right)-y\left(2x-5\right)\)
\(=\left(2x-5\right)\left(x-y\right)\)
\(b,8x^2+4xy-2ax-ay\)
\(=\left(8x^2-2ax\right)+\left(4xy-ay\right)\)
\(=2x\left(4x-a\right)+y\left(4x-a\right)\)
\(=\left(4x-a\right)\left(2x+y\right)\)
\(c,x^3-4x^2+4x\)
\(=x^3-2x^2-2x^2+4x\)
\(=\left(x^3-2x^2\right)-\left(2x^2-4x\right)\)
\(=x^2\left(x-2\right)-2x\left(x-2\right)\)
\(=\left(x-2\right)\left(x^2-2x\right)=x\left(x-2\right)\left(x-2\right)\)
\(=x\left(x-2\right)^2\)
\(d,2xy-x^2-y^2+16\)
\(=-\left(x^2-2xy+y^2-16\right)\)
\(=-\left[\left(x-y\right)^2-4^2\right]\)
\(=-\left(x-y-4\right)\left(x-y+4\right)\)
\(e,x^2-y^2-2yz-z^2\)
\(=x^2-\left(y^2+2yz+z^2\right)\)
\(=x^2-\left(y+z\right)^2=\left(x-y-z\right)\left(x+y+z\right)\)
3 tháng 10 2017
Bài 1 câu g bạn kia làm sai mình sửa lại nhá
\(3a^2-6ab+3b^2-12c^2\)
\(=3\left(a^2-2ab+b^2\right)-12c^2\)
\(=3\left(a-b\right)^2-12c^2\)
\(=3\left[\left(a-b\right)^2-4c^2\right]\)
\(=3\left(a-b-2c\right)\left(a-b+2c\right)\)
3 tháng 10 2017
Để mình làm tiếp cho :))
Bài 2 :
Câu a : \(37,5.8,5-7,5.3,4-6,6.7,5+1,5.37,5\)
\(=\left(37,5.8,5+1,5.37,5\right)-\left(7,5.3,4+6,6.7,5\right)\)
\(=37,5\left(8,5+1,5\right)-7,5\left(3,4+6,6\right)\)
\(=37,5.10-7,5.10\)
\(=10.30=300\)
Câu b : \(35^2+40^2-25^2+80.35\)
\(=\left(35^2+80.35+40^2\right)-25^2\)
\(=\left(30+45\right)^2-25^2\)
\(=75^2-25^2\)
\(=\left(75+25\right)\left(75-25\right)\)
\(=100.50=5000\)
Bài 3 :
Câu a : \(x^3-\dfrac{1}{9}x=0\)
\(\Leftrightarrow x\left(x^2-\dfrac{1}{9}\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x^2-\dfrac{1}{9}=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=\pm\dfrac{1}{3}\end{matrix}\right.\)
Câu b : \(2x-2y-x^2+2xy-y^2=0\)
\(\Leftrightarrow2\left(x-y\right)-\left(x-y\right)^2=0\)
\(\Leftrightarrow\left(x-y\right)\left(2-x+y\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-y=0\\2-x+y=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=y\\x+y=2\Rightarrow x=2-y\end{matrix}\right.\)
Câu c :
\(x\left(x-3\right)+x-3=0\)
\(\Leftrightarrow\left(x-3\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\x+1=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\\x=-1\end{matrix}\right.\)
\(x^2\left(x-3\right)+27-9x=0\)
\(\Leftrightarrow x^2\left(x-3\right)-9\left(x-3\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left(x^2-9\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\x^2-9=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=3\\x=\pm3\end{matrix}\right.\)
Bài 4 :
Câu a :
\(x^2-4x+3\)
\(=x^2-x-3x+3\)
\(=\left(x^2-x\right)-\left(3x-3\right)\)
\(=x\left(x-1\right)-3\left(x-1\right)\)
\(=\left(x-1\right)\left(x-3\right)\)
Câu b :
\(x^2+x-6\)
\(=x^2-2x+3x-6\)
\(=x\left(x-2\right)+3\left(x-2\right)\)
\(=\left(x-2\right)\left(x+3\right)\)
Câu c :
\(x^2-5x+6\)
\(=x^2-2x-3x+6\)
\(=\left(x^2-2x\right)-\left(3x-6\right)\)
\(=x\left(x-2\right)-3\left(x-2\right)\)
\(=\left(x-2\right)\left(x-3\right)\)
Câu d :
\(x^4+4\)
\(=x^4+4x^2+4-4x^2\)
\(=\left(x^2+2\right)^2-\left(2x\right)^2\)
\(=\left(x^2+2-2x\right)\left(x^2+2+2x\right)\)
a) Cậu hình như chép thiếu đề
b) \(35^2+40^2-25^2+80.35\)
= 352 +2.40.35 +402 -252
= (35 +40)2 - 252
= ( 35+40-25).(35+40+25)
=100.50
=5000