Answer:
The third choice is correct
Step-by-step explanation:
The given expression is
[tex]2^n-1[/tex]
when n=7, we substitute into the formula to obtain;
[tex]2^7-1[/tex]
Note that;
[tex]2^7=2\times 2\times 2\times 2\times 2\times 2\times 2=128[/tex]
[tex]2^7-1=128-1=127[/tex]
The third choice is correct
