$\left(x^2-6y^2\right)+\left(-7xy+40y^2\right)$

$2\log\left(x\right)=\log\left(4\right)$

$-8\left(-9r-1\right)-9\left(-8r+2\right)$

$-\left(-9\right)-13+\left(-8\right)-\left(4\right)$

$\left(8x^5y^3-9x^4y^6\right)^2$

$4\cdot x=18.8$

$\frac{d}{dx}\left(\left(x+y\right)^{0.5}=x\right)$