Bài 2:
a: \(A^2=\left(2x+y\right)\left(2x+y\right)\)
\(=4x^2+2xy+2xy+y^2=4x^2+4xy+y^2\)
b: \(B^2=\left(x-2y\right)^2=x^2-4xy+4y^2\)
c: CD
\(=\left(3x+1\right)\left(3x-1\right)\)
\(=9x^2-3x+3x-1=9x^2-1\)
Bài 3:
a: \(\left(5x-2\right)\left(x+1\right)=5x^2\)
=>\(5x^2+5x-2x-2=5x^2\)
=>3x-2=0
=>3x=2
=>\(x=\dfrac{2}{3}\)
b: \(\left(3-x\right)\left(x-4\right)+\left(x-1\right)\left(x-1\right)=10\)
=>\(3x-12-x^2+4x+x^2-2x+1=10\)
=>5x-11=10
=>5x=21
=>\(x=\dfrac{21}{5}\)
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