a) 9x-18= -63
9x= -63+18
9x= -45
x= -5
b) 5x+15=10x-10
5x-10x= -10-15
-5x= -25
x=5
c) 8x+2=10x-14
8x-10x= -14-2
-2x= -16
x= 8
d) -2x+10= -24x-16+56
-2x+24x= 40-10
22x=30
x=15/11
e) 4*[-5(x-2)]= -20
-5(x-2)= -5
x-2= 1
x=3
f) 5x-10-7x-21+35=0
-2x-31+35=0
-2x+4=0
-2x= -4
x=2
g) x^2-7x+3x-21=0
x^2-4x-21=0
delta=16+84=100
x1=(4+10)/2=14/2=7
x2=(4-10)/2= -6/2= -3 => x={-3, 7}
h) -2x^2-6x+6x+18=0
-2x^2+18=0
2(-x^2+9)=0
-x^2+9=0
-x^2= -9
x^2=9
x= -3 sau 3
