Question

Add −2x2+5xy+4y2, x2−2xy+y2

and 3x2+4xy−y2​

Answer 1

$\rm{\left(-2x^2+5xy+4y^2\right)+\left(x^2-2xy+y^2\right)+\left(3x^2+4xy-y^2\right)}$

$\rm{=-2x^2+5xy+4y^2+x^2-2xy+y^2+3x^2+4xy-y^2}$

$\rm{=-2x^2+x^2+3x^2+5xy-2xy+4xy+4y^2+y^2-y^2}$

$\rm{=2x^2+5xy-2xy+4xy+4y^2+y^2-y^2}$

$\rm{=2x^2+7xy+4y^2+y^2-y^2=2x^2+7xy+4y^2}$