Đề bài: Viết tổng thành tích ( theo hằng đẳng thức đáng nhớ )
1. x mũ 2 - 6x + 9
2. x mũ 2 - 2x + 1 - y mũ 2
3. 4x mũ 2 + 12xy + 9y mũ 2
4. 4x mũ 2 + 4x + 1
5. 1/4x mũ 2 - 2/3xy + 4/9 y mũ 2
6. 4a mũ 2 - 4/3ab + 1/9b mũ 2
7. 9x mũ 2 + 4xy + 4/9y mũ 2 - 25z mũ 2
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4. 4x2 + 4x + 1 = ( 2x + 1)2
5. \(\dfrac{1}{4}x-\dfrac{2}{3}xy+\dfrac{4}{9}y^2\) \(=\left(\dfrac{1}{2}x\right)^2-2.\dfrac{1}{2}x.\dfrac{2}{3}+\left(\dfrac{2}{3}y\right)^2\)
\(=\left(\dfrac{1}{2}x-\dfrac{2}{3}y\right)^2\)
6. \(4a^2-\dfrac{4}{3}ab+\dfrac{1}{9}b^2=\left(2a\right)^2-2.2a.\dfrac{1}{3}+\left(\dfrac{1}{3}b\right)^2=\left(2a-\dfrac{1}{3}b\right)^2\)
7.
\(9x^2+4xy+\dfrac{4}{9}y^2-25z^2=\left(3x+\dfrac{2}{3}y\right)^2-\left(5z\right)^2=\left(3x+\dfrac{2}{3}y-5z\right)\left(3x+\dfrac{2}{3}y+5z\right)\)
x2 - 6x + 9 = (x-3)2
x2 - 2x + 1 - y2 = ( x-1)2 - y2 = ( x-1-y)(x-1+y)
4x2 +12xy +9y2 = ( 2x+3y)2
\(4.4x^2+4x+1\)
\(=\left(2x+1\right)^2\)
\(5.\dfrac{1}{4}x^2-\dfrac{2}{3}xy+\dfrac{4}{9}y^2\)
\(=\left(\dfrac{1}{2}x-\dfrac{2}{3}y\right)^2\)
\(6.4a^2-\dfrac{4}{3}ab+\dfrac{1}{9}b^2\)
\(=\left(2a-\dfrac{1}{3}b\right)^2\)