Bài 1:
a: \(=\left(x+\dfrac{1}{2}y\right)^2-16=\left(x+\dfrac{1}{2}y-4\right)\left(x+\dfrac{1}{2}y+4\right)\)
b: \(=x\left(x^2+xy-2y^2\right)=x\left(x^2+2xy-xy-2y^2\right)\)
\(=x\left[x\left(x+2y\right)-y\left(x+2y\right)\right]\)
\(=x\left(x+2y\right)\left(x-y\right)\)
c: \(=\left(x-y\right)\left(x+y\right)+9\left(y-x\right)=\left(x-y\right)\left(x+y-9\right)\)
d: \(=\left(x-y\right)\left(x+y\right)+3\left(x+y\right)=\left(x+y\right)\left(x-y+3\right)\)
Đúng 2
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