Bài 1:
a) 5^x=125
<=>5^x=5^3
<=>x=3
b) 3^2x=81
<=>3^2x=3^4
<=>2x=4
<=>x=2
c) 5^2x-3 - 2.5^2= 5^2 . 3
<=>5^2x-3-2.25=25.3
<=>5^2x-3=75+50
<=>5^2x-3=5^3
<=>2x=3+3
<=>2x=6
<=>x=3
Bài 2:
a) 5^6 : 5^x= 625
<=>5^-x+6=5^4
<=>-x+6=4
<=>-x=4-6
<=>-x=-2
<=>x=2
b) x^3= 216
<=>x^3=6^3
<=>x=6
c) x^3 = x^2
<=>x^3-x^2=0
<=>x^2.(x-1)=0
<=>x^2=0
x-1=0
<=>x=0
x=1