Многочлены (решите уравнение) (3x-+1)=21 5-7x=11x-3(x+5)

(3x - 8) - (7x + 1) = 21
3x - 8 - 7x - 1 = 21
-4x - 9 = 21
-4x = 21 + 9
-4x = 30
x = -30:4
x = -7,5

5 - 7x = 11x - 3(x + 5)
5 - 7x = 11x - 3x - 15
-7x - 11x + 3x = -15 - 5
-15x = -20
15x = 20
x = 20:15
x = 4/3 = 1 1/3 

(3х-8)-(7х+1)=21
3х-8-7х-1=21
3х-7х=21+1+8
-4х=30
х=30:(-4)
х=-7,5
Проверка
((3*-7,5)-8))-((7*-7,5))+1)=21
(-22,5-8)-(-52,5+1)=21
-30,5+51,5=21
21=21

5-7х=11х-3(х+5)
5-7х=11х-3х-15
-7х-11х+3х=-5-15
-15х=-20
х=-20:(-15)
х=20/15=4/3=1.1/3