\[\boxed{\text{970.}\text{\ }еуроки - ответы\ на\ пятёрку}\]
\[\textbf{а)}\ (6x - 1)(6x + 1) -\]
\[- (12x - 5)(3x + 1) =\]
\[= 36x^{2} - 1 -\]
\[- \left( 36x^{2} + 12x - 15x - 5 \right) =\]
\[= 36x^{2} - 1 - 36x^{2} - 12x +\]
\[+ 15x + 5 = 3x + 4\]
\[если\ \ x = 0,2:\]
\[3 \cdot 0,2 + 4 = 0,6 + 4 = 4,6.\]
\[\textbf{б)}\ (5 + 2x)^{2} = 2,5x(8x + 7) =\]
\[= 25 + 20x + 4x^{2} - 20x^{2} -\]
\[- 17,5x =\]
\[= 25 + 2,5x - 16x^{2}\]
\[если\ \ x = - 0,5:\ \]
\[25 - 2,5 \cdot 0,5 - 16 \cdot (0,5)^{2} =\]
\[= 25 - 1,25 - 4 = 19,75.\]