Phân tích đa thức thành nhân tử với dạng thêm bớt khi số mũ chia 3 dư 1, số mũ chia 3 dư 2:
1. x4 - 3x2 + 9
2. x4 + 3x2 + 4
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\(118^2-118.36+18^2\)
\(=118^2-2.118.18+18^2\)
\(=\left(118-18\right)^2\)
\(=100^2=10000\)
\(118^2-118.36+18^2\)
=\(118^2-2.118.18+18^2\)
=\(\left(118-18\right)^2\)
=\(100^2\)
Bài 1:
a) \(2x^2y-xy=xy\left(2x-1\right)\)
b)\(2x^2-x-2y^2-y=\left(2x^2-2y^2\right)-\left(x+y\right)\)
\(=2\left(x^2-y^2\right)-\left(x+y\right)\)
\(=2\left(x-y\right)\left(x+y\right)-\left(x+y\right)\)
\(=\left(x+y\right)\left(2x-2y-1\right)\)
Bài 2:
a)\(x^3-\frac{1}{9}x=0\)
\(\Leftrightarrow x\left(x^2-\frac{1}{9}\right)=0\)
\(\Leftrightarrow x\left(x-\frac{1}{3}\right)\left(x+\frac{1}{3}\right)=0\)
\(\Rightarrow x=0\text{ hoặc }x-\frac{1}{3}=0\Leftrightarrow x=\frac{1}{3}\text{ hoặc }x+\frac{1}{3}=0\Leftrightarrow x=-\frac{1}{3}\)
Vậy...
b)\(\left(x+1\right)^2=5x\left(x+1\right)\)
\(\Leftrightarrow\left(x+1\right)^2-5x\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x+1-5x\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(-4x+1\right)=0\)
\(\Leftrightarrow-\left(x+1\right)\left(4x-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x+1=0\\4x-1=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-1\\4x=1\Leftrightarrow x=\frac{1}{4}\end{cases}}}\)
Vậy...
a) \(2x^2-50\)
\(=2\left(x^2-25\right)\)
\(=2\left(x-5\right)\left(x+5\right)\)
b) \(x^2z+4xyz+4y^2z\)
\(=z\left(x^2+4xy+4y^2\right)\)
\(=z\left(x+2y\right)^2\)
c) \(x^2-y^2+12y-36\)
\(=x^2-\left(y^2-2\cdot x\cdot6+6^2\right)\)
\(=x^2-\left(y-6\right)^2\)
\(=\left(x-y+6\right)\left(x+y-6\right)\)
d) Đặt \(D=x\left(x+1\right)\left(x+2\right)\left(x+3\right)+1\)
\(D=\left[x\left(x+3\right)\right]\left[\left(x+1\right)\left(x+2\right)\right]+1\)
\(D=\left(x^2+3x\right)\left(x^2+3x+2\right)+1\)
Đặt \(x^2+3x+1=a\)
\(D=\left(a-1\right)\left(a+1\right)+1\)
\(D=a^2-1^2+1\)
\(D=a^2\)
Thay \(x^2+3x+1=a\)vào D ta có :
\(D=\left(x^2+3x+1\right)^2\)
a: \(2x^2-50=2\left(x^2-5^2\right)\)
\(=2\left(x-5\right)\left(x+5\right)\)
b:\(x^2z+4xyz+4y^2z=z\left(x^2+4xy+4y^2\right)\)
\(=z\left(x+2y\right)^2\)
c:\(x^2-y^2+12y-36=x^2-\left(y^2-12y+36\right)\)
\(=x^2-\left(y-6\right)^2\)
\(=\left(x-y+6\right)\left(x+y-6\right)\)
d:\(x\left(x+1\right)\left(x+2\right)\left(x+3\right)+1=x\left(x+3\right)\left(x+1\right)\left(x+2\right)+1\)
\(=\left(x^2+3x\right)\left(x^2+3x+2\right)+1\)
Đặt \(t=x^2+3x+1\)Ta có:
\(=\left(t-1\right)\left(t+1\right)+1\)
\(=t^2-1+1=t^2\)
\(=\left(x^2+3x+1\right)^2\)
\(x^4-3x^2+9\)
\(=\left(x^2\right)^2+2.x^2.3+3^2-9x^2\)
\(=\left(x^2+3\right)^2-\left(3x\right)^2\)
\(=\left(x^2-3x+3\right)\left(x^2+3x+3\right)\)
\(x^4+3x^2+4\)
\(=\left(x^2\right)^2+2.x^2.2+2^2-x^2\)
\(=\left(x^2+2\right)^2-x^2\)
\(=\left(x^2-x+2\right)\left(x^2+x+2\right)\)