1) Ta có: \(\left(x+y+2\right)^2\)
\(=x^2+y^2+4+2xy+2\cdot x\cdot2+2\cdot y\cdot2\)
\(=x^2+y^2+4+2xy+4x+4y\)
2) Ta có: \(\left(x-2y+3\right)^2\)
\(=x^2+4y^2+9-2\cdot x\cdot2y+2\cdot x\cdot3-2\cdot2y\cdot3\)
\(=x^2+4y^2+9-4xy+6x-12y\)
3) Ta có: \(\left(x^2-y-4\right)^2\)
\(=x^4+y^2+16+2\cdot x^2\cdot\left(-y\right)+2\cdot x^2\cdot\left(-4\right)+2\cdot\left(-y\right)\cdot\left(-4\right)\)
\(=x^4+y^2+16-2x^2y-8x^2+8y\)
4) Ta có: \(100x^2-\left(x^2+25\right)\)
\(=100x^2-x^2-25\)
\(=99x^2-25\)
5) Ta có: \(\left(x-3\right)^2-16\)
\(=x^2-6x+9-16\)
\(=x^2-6x-7\)
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