Question

-x²+13y²-5y+7x²-8y²+2y²​

Answer 1

$\sf{-x^2+13y^2-5y+7x^2-8y^2+2y^2}$

$\bf{Group\:like\:terms}$

$\sf{=13y^2-8y^2+2y^2-5y-x^2+7x^2}$

$\bf{\bf{Add\:similar\:elements:}\:-x^2+7x^2=6x^2}$

$\sf{=13y^2-8y^2+2y^2-5y+6x^2}$

$\bf{\bf{Add\:similar\:elements:}\:13y^2-8y^2+2y^2=7y^2}$

$\sf{=7y^2-5y+6x^2}$