It appears that you've made a small calculation error when calculating the value for $c$ when using the pythagorean theorem (second image).
The correct expansion is $(2x+1)^2=4x^2+4x+\mathbf{1}$, where you wrote $4x^2+4x+\mathbf{2}$.
Just as a side note, it would be greatly preferred if you use mathjax or an alternative rather than uploading a plain picture of your work. I understand that it's pretty time consuming and sometimes frustrating to type up everything, but it was pretty difficult to read some of your work.
Perhaps you could use an app like Genius Scan to make your images clearer?