Different Ground State Energy in Tinkham's Superconductivity?

[asheg]

Homework Statement

In "Introduction to superconductivity" by Tinkham, in section 3.4.2 he calculates ground state energy. I get different result when I calculate it

My calculated Ground State Energy
$$E = ... - 2*\frac{\Delta^2}{V}$$

But in the book
$$E = ... - \frac{\Delta^2}{V}$$

Homework Equations

$$\frac{2}{V} = \sum\frac{1}{E_k}$$

The Attempt at a Solution

My calculated Ground State Energy
$$E = ... - 2*\frac{\Delta^2}{V}$$
because of
$$\frac{2}{V} = \sum\frac{1}{E_k}$$
and if we insert it into energy equation a "2" will be there.

 

[fzero]

There's a factor of 2 in eq (3.29b) that cancels the factor of 2 that you have.

 

[asheg]

There's a factor of 2 in eq (3.29b) that cancels the factor of 2 that you have.

Thank you fzero for your help.
But I'm not sure that my fault be there since that 2 is in nominator not in denominator.