5.122 Найдите корень уравнения и выполните проверку: a) -30(x - 21) = -180; б) (15 - 9x)4 = 204; в) 9/4 x - 1/14 = 7; г) (3,6 - 0,2x)4,9 = 9,8; д) (7х - 3,4)9 = 13,5; e) 1/3 x + 5/6 x = 3,5.

a) -30x + 630 = -180 => -30x = -810 => x = 27.
б) 60 - 36x = 204 => -36x = 144 => x = -4.
в) 9/4 x = 7 + 1/14 => 9/4 x = 99/14 => x = 99/14 * 4/9 = 11/7 * 2 = 22/7.
г) 17.64 - 0.98x = 9.8 => -0.98x = -7.84 => x = 8.
д) 63x - 30.6 = 13.5 => 63x = 44.1 => x = 0.7.
e) 2/6 x + 5/6 x = 3.5 => 7/6 x = 3.5 => x = 3.5 * 6/7 = 0.5 * 6 = 3.