a) `3^(x-1) + 5. 3^(x-1) = 162`
`=> 3^(x-1) ( 1 + 5) =162`
`=> 3^(x-1) .6 = 162`
`=> 3^(x-1) = 162 :6`
`=> 3^(x-1) = 27`
`=> 3^(x-1) = 3^3`
`=> x-1=3`
`=> x= 3+1`
`=> x=4`
Vậy `x= 4`
b) `2^(x+3) + 2^x =144`
`=> 2^x . 2^3 + 2^x = 144`
`=> 2^x .8 + 2^x .1=144`
`=> 2^x( 8+1) =144`
`=> 2^x . 9 = 144`
`=> 2^x = 144 :9`
`=> 2^x = 16`
`=> 2^x =2^4`
`=>x=4`
Vậy `x= 4`