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Lê Trinh
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Lucchiki
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Trần Mạnh
18 tháng 2 2021 lúc 21:06

 a) 3x2 – 7x + 2

\(=3x^2-6x-x+2\)

\(=\left(3x^2-6x\right)-\left(x-2\right)\)

\(=3x\left(x-2\right)-\left(x-2\right)\)

\(=\left(x-2\right)\left(3x-1\right)\)

 b) a(x2 + 1) – x(a2 + 1)

\(=ax^2+a-\left(a^2x+x\right)\)

\(=a\left(x^2+1\right)-x\left(a^2+1\right)\)

.......?

 

 

 

 

Nguyễn Lê Phước Thịnh
18 tháng 2 2021 lúc 21:10

a) Ta có: \(3x^2-7x+2\)

\(=3x^2-6x-x+2\)

\(=3x\left(x-2\right)-\left(x-2\right)\)

\(=\left(x-2\right)\left(3x-1\right)\)

b) Ta có: \(a\left(x^2+1\right)-x\left(a^2+1\right)\)

\(=x^2a+a-a^2x-x\)

\(=\left(x^2a-a^2x\right)+\left(a-x\right)\)

\(=xa\left(x-a\right)-\left(x-a\right)\)

\(=\left(x-a\right)\left(xa-1\right)\)

c) Ta có: \(\left(x+2\right)\left(x+3\right)\left(x+4\right)\left(x+5\right)-24\)

\(=\left(x^2+7x+10\right)\left(x^2+7x+12\right)-24\)

\(=\left(x^2+7x\right)^2+22\left(x^2+7x\right)+120-24\)

\(=\left(x^2+7x\right)^2+22\left(x^2+7x\right)+96\)

\(=\left(x^2+7x\right)^2+16\left(x^2+7x\right)+6\left(x^2+7x\right)+96\)

\(=\left(x^2+7x\right)\left(x^2+7x+16\right)+6\left(x^2+7x+16\right)\)

\(=\left(x^2+7x+16\right)\left(x^2+7x+6\right)\)

\(=\left(x^2+7x+16\right)\left(x+1\right)\left(x+6\right)\)

d) Ta có: \(\left(a+1\right)\left(a+3\right)\left(a+5\right)\left(a+7\right)+15\)

\(=\left(a^2+8a+7\right)\left(a^2+8a+15\right)+15\)

\(=\left(a^2+8a\right)^2+22\left(a^2+8a\right)+105+15\)

\(=\left(a^2+8a\right)^2+22\left(a^2+8a\right)+120\)

\(=\left(a^2+8a\right)^2+12\left(a^2+8a\right)+10\left(a^2+8a\right)+120\)

\(=\left(a^2+8a\right)\left(a^2+8a+12\right)+10\left(a^2+8a+12\right)\)

\(=\left(a^2+8a+12\right)\left(a^2+8a+10\right)\)

\(=\left(a+2\right)\left(a+6\right)\left(a^2+8a+10\right)\)

Thaoperdant
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Nguyễn Thị Anh Trâm
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marie
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Nguyễn Hoàng Thái Phát
7 tháng 7 2022 lúc 19:52

a) x2 - 7x + 5 = ( x2 - 2 . 7/2 . x + 49 / 4 ) + 5 - 49 / 4 
= (x - 7/2)^2 - 29/4
= (x - 7/2)^2 - (√ 29 / 2 )^2
= ( x - ( 7 + √ 29 / 2 )). ( x + ( 7 - √ 29 / 2 ))

Trần Linh Nga
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nguyen thi vang
8 tháng 8 2018 lúc 18:39

1) \(x^2-8x+7=0\)

\(\Leftrightarrow x^2-7x-x+7=0\)

\(\Leftrightarrow\left(x^2-7x\right)-\left(x-7\right)=0\)

\(\Leftrightarrow x\left(x-7\right)-\left(x-7\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x-7\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x-7=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=7\end{matrix}\right.\)

2) \(5x^2-11x+6=0\)

\(\Leftrightarrow5x^2-5x-6x+6=0\)

\(\Leftrightarrow\left(5x^2-5x\right)-\left(6x-6\right)=0\)

\(\Leftrightarrow5x\left(x-1\right)-6\left(x-1\right)=0\)

\(\Leftrightarrow\left(5x-6\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}5x-6=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{6}{5}\\x=1\end{matrix}\right.\)

3) \(2x^2-3x+1=0\)

\(\Leftrightarrow2x^2-2x-x+1=0\)

\(\Leftrightarrow\left(2x^2-2x\right)-\left(x-1\right)=0\)

\(\Leftrightarrow2x\left(x-1\right)-\left(x-1\right)=0\)

\(\Leftrightarrow\left(2x-1\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-1=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{2}\\x=1\end{matrix}\right.\)

4) \(x^2+7x-8=0\)

\(\Leftrightarrow x^2+8x-x-8=0\)

\(\Leftrightarrow\left(x^2+8x\right)-\left(x+8\right)=0\)

\(\Leftrightarrow x\left(x+8\right)-\left(x+8\right)=0\)

\(\Leftrightarrow\left(x-1\right)\left(x+8\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-1=0\\x+8=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-8\end{matrix}\right.\)

5) \(3x^2+7x-10=0\)

\(\Leftrightarrow3x^2-3x+10x-10=0\)

\(\Leftrightarrow\left(3x^2-3x\right)+\left(10x-10\right)=0\)

\(\Leftrightarrow3x\left(x-1\right)+10\left(x-1\right)=0\)

\(\Leftrightarrow\left(3x+10\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}3x+10=0\\x-1=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-\dfrac{10}{3}\\x=1\end{matrix}\right.\)

Hắc Hàn Nan Thiên
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Trần Linh Nga
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nguyen thi vang
8 tháng 8 2018 lúc 18:50

Phân tích đa thức thành nhân tử:

1. x2 - 5x - 6

\(=x^2-6x+x-6\)

\(=\left(x^2-6x\right)+\left(x-6\right)\)

\(=x\left(x-6\right)+\left(x-6\right)\)

\(=\left(x+1\right)\left(x-6\right)\)

3. 1 + 3x + 2x2

\(=1+2x+x+2x^2\)

\(=\left(1+2x\right)+\left(x+2x^2\right)\)

\(=\left(1+2x\right)+x\left(1+2x\right)\)

\(=\left(1+2x\right)+\left(x+1\right)\)

4. 6 - 2x - 8x2

\(=6-8x+6x-8x^2\)

\(=\left(6+6x\right)-\left(8x+8x^2\right)\)

\(=6\left(1+x\right)-8x\left(1+x\right)\)

\(=\left(6-8x\right)\left(1+x\right)\)

5. 7 - 4x - 3x2

\(=7-7x+3x-3x^2\)

\(=\left(7-7x\right)+\left(3x-3x^2\right)\)

\(=7\left(1-x\right)+3x\left(1-x\right)\)

\(=\left(7+3x\right)\left(1-x\right)\)

Nguyễn Trần Thành Đạt
8 tháng 8 2018 lúc 17:25

1) \(x^2-5x-6\\ =x^2+x-6x-6\\ =x\left(x+1\right)-6\left(x+1\right)\\ =\left(x-6\right)\left(x+1\right)\)

3) \(1+3x+2x^2\\ =2x^2+2x+x+1\\ =2x\left(x+1\right)+\left(x+1\right)\\ =\left(x+1\right)\left(2x+1\right)\)

nguyên công quyên
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