$$\frac{sen\:a}{cos\:ec\:a}+\frac{cos\:a}{sec\:a}=1$$

$$sin\left(x\right)\cdot\:\sin\:\left(x-y\right)+cos\:\left(x\right)\cdot\:cos\:\left(x-y\right)=cos\:\left(y\right)$$

$$\lim_{x\to0}\left(\frac{\sqrt{x+2}-\sqrt{2}}{\sqrt{2}.x}\right)$$

$$2.2\left(4.7x\:+\:1.5y\right)-3.4\left(5x\:-\:2.7y\right)-\left(6.2x\:-\:7y\right)$$

$$\left(7x^2+y\right)^2$$

$$38a^2b^3-\left(15a^2b^3\right)$$

$$3x+2y-3z+5w=-2$$