Bài 1: Tìm x
a) x+ 3/10 = 17/12 -17/20
b) x/20 = 7/12 + 11/30
c) 3 – ( 17- x ) = 289
Bài 2
A= 1/2² + 1/3² + 1/4² +…..+1/9²
Chứng tỏ 8/9 > A > 2/5
Bài 3
So sánh 7/4 và 11/-6
Bài 1: Tìm x a) x+ 3/10 = 17/12 -17/20 b) x/20 = 7/12 + 11/30 c) 3 – ( 17- x ) = 289 Bài 2 A= 1/2² + 1/3² + 1/4² +…..+1/9² Chứng tỏ 8/9 > A > 2/5
By Mackenzie
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