X+78+X=198
<=> 2X=120
<=> X=60
798-X×9×2=150
<=> -X×18=-648
<=> -X=-11664
<=> X=11664
9X (X+5) =378
<=> 9X^2 + 45X =378
<=> X1=4,446221995
X2=-9,446221995
x + 78 + x = 196
2x + 78 = 196
2x = 196 - 78
2x = 118
x = 118 : 2
x = 59
x+78+x=196 vậy x= 60
798-X x 9 x2 =150 vậy X =36
9 x( x+ 5) =378 vậy x= 37