5^(x-2)-5^(x-1)+5^x=21

Question

5^(x-2)-5^(x-1)+5^x=21

Answer 1

5^x * 1/25 - 5^x*1/5 + 5^x = 21
5^x ( 1/25 - 1/5 + 1) = 21
5^x (1/25 - 5/25 + 25/25) = 21
5^x *21/25 = 21  
домножим на 25/21, получим
5^x = (21*25)/21 
5^x = 25
5^x = 5^2
x = 2