$\left(0.7x-1.5y\right)\left(0.7x+1.5y\right)$

$3.n=51$

$b^2-10b+25$

$\left(\frac{1}{2}x+\frac{3}{4}\right)\left(\frac{1}{2}x-\frac{3}{4}\right)$

$\frac{\cos\left(2x\right)}{\cos\left(x\right)^2+\sin\left(x\right)\cos\left(x\right)}=1-\tan\left(x\right)$

$xy^3dx+e^{x^2}dy=0$

$\frac{9b^3-12b}{-3b^2}$