$x^3+28y^3+3xy\left(x+y\right)$

$\frac{\left(x^2+2x-63\right)}{\left(x+9\right)}$

$169x^4-13x^2y^2+\frac{y^2}{4}$

$\frac{\sin\left(x\right)^4-\sin\left(x\right)^6}{cos\left(x\right)^4-\cos\left(x\right)^6}$

$e^2.1$

$x^4-169$

$\frac{d^2}{dx^2}\left(14x^3-32x^4\right)$