16c-12-10c-8 = 6c-20
При c=5/6
6*5/6-20= 5 - 20= -15
1/27 = 3^(-3).
Получим неравенство х≥-3. Ответ: (-3;+∞).
1. b) (2/(7y+x))(x-2/7y) =
2*(x-2) /(7y+x)*7y =(2x-4)/(49y²+7xy)
a) (4x-0.2y)² =16x² -1.6xy +0.04y²
2. (x-2)(x+2) -(x-1)² =x² -5
x² -4 -(x² -2x +1) =x² -5
x² -4 -x² +2x -1 =x² -5
2x -5 =x² -5
-x² +2x -5 +5 =0
2x -x² =0
x(2 -x) =0
x =0
2 -x =0
x =2
3. (a² +10a +25)/(a +5) при a =2.5
(a +5)² /(a +5) =a +5 =2.5 +5 =7.5