Решите 5 и 7 и из 17 3 Пожалуйста

5)
$x - {11x}^{2} = 0 \\ x(1 - 11x) = 0 \\ x = 0 \: u \: 1 - 11x = 0 \\ - 11x = - 1 \\ x = \frac{ - 1}{ - 11} \\ x = \frac{1}{11}$
х = 0 и х = 1/11.

7)
${2n}^{2} = 7n + 9 \\ {2n}^{2} - 7n - 9 = 0$
a=2, b=-7, c=-9.
т.к. b=a+c, то х=-1; х=-с/а=9/2=4,5.

3)
${9x}^{2} + 6 = 21x \\ {9x}^{2} - 21x + 6 = 0 \\ {3x}^{2} - 7x + 2 = 0 \\ {3x}^{2} - x - 6x + 2 = 0 \\ x(3x - 1) - 2(3x - 1) = 0 \\ (x - 2)(3x - 1) = 0 \\ x - 2 = 0 \: u \: 3x - 1 = 0 \\x = 2 \: u \: x = \frac{1}{ 3}$
х=2 и х=1/3.