$\lim_{x\to-\infty}\left(\frac{3x^2+9x}{x^2-9}\right)$

$\int5\left(5x+1\right)^2dx$

$x^4-2x^3+4x^2$

$\left(a\cdot a\right)+5\left(a\cdot a\right)+3\left(b\cdot b\right)+2\left(a\cdot a\right)-5\left(b\cdot b\right)$

$\int\left(9t+1\right)\left(4e^{2t}-3sin3t\right)dt$

$\frac{1}{1+k}\le0.05$

$4<2x-3$