cuanto es (0,7+2x)(0,7-2x)

$$\left({\mathtt{a}}{\mathtt{\,\small\textbf+\,}}{\mathtt{b}}\right){\mathtt{\,\times\,}}\left({\mathtt{a}}{\mathtt{\,-\,}}{\mathtt{b}}\right) = {{\mathtt{a}}}^{{\mathtt{2}}}{\mathtt{\,-\,}}{{\mathtt{b}}}^{{\mathtt{2}}}$$

Entonces, (0.7 +2 x) (0.7-2x)

= 0.7^2 - (2x)^2

= 0.49 - 4x²