Explanation with constructive Scenario:
Just assume that the par value of the stock is $1 per share and the company has issued initially 1000 share at $2 which means the total cash received is $2,000. Now assume that these 1000 shares were reacquired at $1.5.
The double entry using the cost method would be as under:
Dr Treasury Shares $1,500
Cr Cash Account $1,500
The re-acquisition under the par value method would be as under:
Dr Treasury shares (at the rate $1) $1,000
Cr Additional paid-in capital (at the rate $2 - $1) $500
Cr Cash Account $1,500
Answer: This shows that under he par value method the additional paid-in capital is reduced by the amount paid above the par value, whereas the retained earnings remains the same.