2)a) Ta có: 20/45=4/9; 14/-35=-2/7; -32/44=-8/11
4/9=4*77/9*77=308/693; -2/7=-2*99/7*99=-198/693; -8/11=-8*63/11*63=-504/693
b) Ta có: -15/90=-1/6; 120/600=1/5; -75/150=-1/2
-1/6=-1*10/6*10=-10/60; 1/5=1*12/5*12=12/60; -1/2=-1*30/2*30=-30/60
c) Ta có: 54/-90=-3/5; -180/288=-5/8; 60/-135=-4/9
-3/5=-3*72/5*72=-216/360; -5/8=-5*45/8*45-225/360; -4/9=-4*40/9*40=-160/360
d) Ta có: 3*4+3*11/9*2+3=15/7; 8*3-3*2/4*7-2*6=9/8
15/7=15*8/7*8=120/56; 9/8=9*7/8*7=63/56
3)a) x/5=x+6/15 b)x+10/27=x/9 c)x+16/35=x/7
x+6/15=1/5 27x=9*(x+10) 16/35=x/7-x
x=1/5-6/15 27x=9x+9*10 16/35=x(1/7-1)
x=-1/5 27x=9x+90 16/35=x(-6/7)
27x-9x=90 x=16/35:(-6/7)
18x=90 x=-8/15
x=90:18
x=5
4) Gọi phân số đó là: a/5, theo đề bài ta có:
a+8/3*5=a/5
5*(a+8)=3*5a
5a+5*8=15a
5a+40=15a
15a-5a=40
10a=40
a=40:10
a=4
Vậy a=4
Nhớ cho mình 5 sao nhé