1.
a)3.(5^x-1)-2=70
=>3.(5^x-1)=72
=>5^x-1=24
=>5^x=25
=>5^x=5^2
=>x=2
Vậy x=2
b)(1/1.2.3+1/2.3.4+1/3.4.5+...+1/8.9.10).x=22/45
=>[1/2.(2/1.2.3+2/2.3.4+2/3.4.5+...+2/8.9.10).x=22/45
=>[1/2.(1/1.2-1/2.3+1/2.3-1/3.4+1/3.4-1/4.5+...+1/8.9-1/9.10).x=22/45
=>[1/2.(1/1.2-1/9.10).x=22/45
=>(1/2.37/45).x=22/45
=>97/90.x=22/45
=>x=22/45:97/90
=>x=44/97
Vậy x=44/97
Chúc bạn hok tốt!!
