$-7a^2,\:5ab,\:3b^2,\:-a^2$

$\left(x+2\right)^2-\:\left(2-x\right)^2+\left(x-4\right)^2-x^2-16$

$10r\:+\:42\:=\:-38$

$-\frac{1}{5}\left(-0.8\right)$

$\lim_{x\to-1}\left(\frac{x^3+2x^2+x}{x^3+x^3+x-1}\right)$

$f\left(x\right)=3x^6+x^2+2x$

$\frac{\left(x^4+3x^3-28x^2+6x-15\right)}{\left(x-4\right)}$