a. $3^{2x + 1}$ . 15 = $3^{6}$ . 5 b.$7^{x + 1}$ + $7^{x + 2}$ = $2^{3}$ . $7^{2}$

Answer.

`a,3^{2x+1}.15=3^6 .5`

`=>3^{2x+1}=3^6 .5:15`

`=>3^{2x+1}=3^6 :3`

`=>3^{2x+1}=3^5`

`=>2x+1=5`

`=>2x=4`

`=>x=2`

Vậy `x=2`

`b,7^{x+1}+7^{x+2}=2^3 .7^2`

`=>7^x .7+7^x .7^2=8.49`

`=>7^x .(7+49)=392`

`=>7^x .56=392`

`=>7^x=7`

`=>7^x=7^1`

`=>x=1`

Vậy `x=1`