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a) x2 + 2x + 1 = x2 + 2.x.1+ 12 = ( x + 1)2
b) 9x2 + y2 + 6xy = (3x)2 + 2.3.x.y + y2 = (3x + y)2
c) 25a2 + 4b2 – 20ab = (5a)2 – 2.5.a.2b. + (2b)2 = (5a – 2b)2
Hoặc 25a2 + 4b2 – 20ab = (2b)2 – 2.2b.5a. + (5a)2 = (2b – 5a)2
d) x2 – x + \(\dfrac{1}{4}\) = x2 – 2.x. \(\dfrac{1}{2}\) + ( \(\dfrac{1}{2}\))22 = ( x - \(\dfrac{1}{2}\) )2
Hoặc x2 – x + \(\dfrac{1}{4}\) = \(\dfrac{1}{4}\) - x + x2 = (\(\dfrac{1}{2}\))2 – 2. \(\dfrac{1}{2}\).x + x2 = (\(\dfrac{1}{2}\) - x)2
a) x2 + 2x + 1 = x2+ 2 . x . 1 + 12
= (x + 1)2
b) 9x2 + y2+ 6xy = (3x)2 + 2 . 3 . x . y + y2 = (3x + y)2
c) 25a2 + 4b2– 20ab = (5a)2 – 2 . 5a . 2b + (2b)2 = (5a – 2b)2
Hoặc 25a2 + 4b2 – 20ab = (2b)2 – 2 . 2b . 5a + (5a)2 = (2b – 5a)2
d) x2 – x + 1414 = x2 – 2 . x . 1212 + (12)2(12)2= (x−12)2(x−12)2
Hoặc x2 – x + 1414 = 1414 - x + x2 = (12)2(12)2 - 2 . 1212 . x + x2 = (12−x)2
a ) \(x^2-6x+9\)
\(=x^2-2.x.3+3^2\)
\(=\left(x-3\right)^2\)
b ) \(25+10x+x^2\)
\(5^2+2.5.x+x^2\)
\(=\left(5+x\right)^2\)
c ) \(\frac{1}{9}-\frac{2}{3}y^4+y^8\)
\(=\left(\frac{1}{3}\right)^2-2.\frac{1}{3}.y^4+\left(y^4\right)^2\)
\(=\left(\frac{1}{3}-x^4\right)^2\)
câu c) sai rùi phải là \(\left(\frac{1}{3}-y^4\right)^2\) chứ 
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a \(x^2-6x+9=x^2-2.3.x+3^2=\left(x-3\right)^2\)
b \(4y^2+y+\frac{1}{16}=\left(2y\right)^2+2.2y.\frac{1}{4}+\left(\frac{1}{4}\right)^2=\left(2y+\frac{1}{4}\right)^2\)
*\(x^2-x+\frac{1}{4}=x^2-2.x.\frac{1}{2}+\left(\frac{1}{2}\right)^2=\left(x-\frac{1}{2}\right)^2\)
*\(25a^2+4b^2-20ab=\left(5a\right)^2-2.5a.2b+\left(2b\right)^2=\left(5a-2b\right)^2\)
*\(9x^2+y^2+6xy=\left(3x\right)^2+2.3x.y+y^2=\left(3x+y\right)^2\)
\(4x^2+4xy+y^2\)
\(=\left(2x\right)^2+2.2x.y+y^2\)
\(=\left(2x+y\right)^2\)
hằng đẳng thức số 1 mà bạn~
a) = x^2 - 2x + 1 + 4y^2 + 4y + 1
= ( x - 1 )^2 + ( 2y + 1 )^2
b) = 4x^2 + 4x +1 + 4y^2 + 4y + 1
= ( 2x + 1 )^2 + ( 2y + 1 )^2
c) = 9x^2 - 12x + 4 + 16y^2 - 24y + 9
=( 3x - 2 )^2 + ( 4y - 3 )^2
d) = 4x^2 + 4xy+ y^2 + x^2 - 2xz + z^2
= ( 2x + y )^2 + ( x - z )^2
a, (x+2)^2
b, (x-3)^2
c, (2x+3)^2
d, (3x-1)^2
e, (x+5)^2
g, (4x-1)^2
a) x2 + 4x + 4 = ( x + 2 )2
b) x2 - 6x + 9 = (x-3)2
c) 4x2 + 12x + 9 = (2x)2 + 2.2x.3 + 3^2 = (2x + 3)2
d) 9x2 - 6x + 1 = (3x)2 - 2.3x.1 + 1^2 = (3x-1)2
e) x2 + 25 +10x = x2 + 2.x.5 + 52 = (x+5)2
g) 16x2 +1 - 8x = (4x)2 - 2.4x.1 + 1^2 = (4x-1)2