1.a.x+3/10=17/12-17/20
x+3/10=17/30
x =17/30-3/10
x =4/15
b.x/20=7/12+11/30
x/20=19/20
x =19
c. 3-(17-x)=289
17-x =3-289
17- x =-286
x =17-(-286)
x =303
2.ta có : 1/1-1/2>1/2^2>1/2-1/3;1/2-1/3>1/3^2>1/3-1/4;...;1/8-1/9>1/9^2>1/9-1/10
1-1/9>1/2^2+1/3^2+1/4^2+...+1/9^2>1/2-1/10
=>8/9>A>2/5
3.7/4 và 11/-6 ; 11/-6=-11/6
MSC:24
7/4=7.6/4.6=42/24 ; -11/6=-11.4/6.4=-44/24
=>42/24>-44/24=>7/4>-11/6