7)
b) 4x+31=2x
2x= -31 →x= -31/2 ∉ N → Ecuatia nu are solutii S=∅ (multimea vida)
c) 9x-13=4*(2x+1) + x - 17
9x+13=8x+1+x-17
9x+13=9x+13
0x=0 →Ecuatia are o infinitate de solutii
d) 6x+10=213
6x=213-10
6x=203
x=203/6 ∉ N → Ecuatia nu are solutii S=∅
9)
a) 2x+7=x+32
2x-x=32-7
x=25
b) 3x-8=x+4
3x-x=8+4
2x=12 /2
x=6
c)4x+5 = x+68
4x-x=68-5
3x=63 /3
x=21
d) 25-3x=17-x
25-17 = 3x+x
8=4x →4=x sau x=4
e)5x+7=23+x
5x-x=23-7
4x=16→x=4
f)6x+10=2x+50
6x-2x=50-10
4x=40→x=10
