Question

B1: rút gọn biểu thức
a)(x+y)²+(x-y)²-2x²
b) (x+2y)(x²-2xy+4y²)
c)(x+2y)(x²-2xy-4y²)-(x-2y)(x²+2xy+4y²)+2y³

Answer 1

\(a,\left(x+y\right)^2+\left(x-y\right)^2-2x^2\)
\(=x^2+2xy+y^2+x^2-2xy+y^2-2x^2\)
\(=2y^2\)
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\(b,\left(x+2y\right)\left(x^2-2xy+4y^2\right)\)
\(=x^3+\left(2y\right)^3\)
\(=x^3-8y^3\)
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\(c,\left(x+2y\right)\left(x^2-2xy+4y^2\right)-\left(x-2y\right)\left(x^2+2xy+4y^2\right)+2y^3\)
\(=x^3+8y^3-\left(x^3-8y^3\right)+2y^3\)
\(=x^3+8y^3-x^3+8y^3+2y^3\)
\(=18y^3\)