Question

What is the solution of
2
(
7
2
x
)
=
686
?

Answer 1

Likely interpretation: 2·7^(2x) = 686.

2·7^(2x) = 686
=> 7^(2x) = 343 = 7^3
=> 2x = 3
=> x = 3/2.

(If you meant 2·(7^2 x) = 686 = 2·49x, then 98x = 686 so x = 7. Which interpretation did you intend?)