$(2x - c)(x + c) - (2c + x)(x - c) + x(2 - x) = 2x^2 - cx - c^2 - (2cx + x^2 - 2c^2 - cx) + 2x - x^2 = 2x^2 - cx - c^2 - 2cx - x^2 + 2c^2 + cx + 2x - x^2 = c^2 + 2x$
при c = 0,7, x = −1:
$c^2 + 2x = 0,7^2 + 2 * (-1) = 0,49 - 2 = -1,51$
при c = −0,2, x = −0,5:
$c^2 + 2x = (-0,2)^2 + 2 * (-0,5) = 0,04 - 1 = -0,96$

$(2x^2 + x + 1)(x - 2) + 2x^2(2 - x) - (x^2 - 1) = 2x^3 + x^2 + x - 4x^2 - 2x - 2 + 4x^2 - 2x^3 - x^2 + 1 = -x - 1$
при x = 0,3:
−x − 1 = −0,3 − 1 = −1,3;
при x = −0,2:
−x − 1 = −(−0,2) − 1 = 0,2 − 1 = −0,8.

$(a^2 - 2a + 3)(a - 3) - 9(a - 1) + a(5a + 6) = a^3 - 2a^2 + 3a - 3a^2 + 6a - 9 - 9a + 9 + 5a^2 + 6a = a^3 + 6a$
при $a = -\frac{1}{2}$:
$a^3 + 6a = (-\frac{1}{2})^3 + 6 * (-\frac{1}{2}) = -\frac{1}{8} - 3 = -3\frac{1}{8}$;
при $a = \frac{1}{3}$:
$a^3 + 6a = (\frac{1}{3})^3 + 6 * \frac{1}{3} = \frac{1}{27} + 2 = 2\frac{1}{27}$