5n + 7 = 7(n+1) - 2n
First distribute 7 to all terms inside the parenthesis
7(n) = 7n
7(1) = 7
5n + 7 = 7n - 2n + 7
Simplify. Combine like terms
5n + 7 = 5n + 7
True.
If you want to continue:
Isolate the n, move all variables to one side, and constants to the other
5n (-5n) + 7 (-7) = 5n (-5n) + 7 (-7)
0 = 0
True
hope this helps