For the given parallelogram to be a square, its diagonals should be equal. Let's put more details in the given figure to better understand:
Naming the two diagonals to be AC and BD, for it to be a square,
![\text{ AC = BD}](https://img.qammunity.org/2023/formulas/mathematics/college/40ryds6wvsbt0lbi3bg4yn7xygw4qnwj4w.png)
AC = 12x - 23
BD = 4x + 17
We get,
![\text{ AC = BD}](https://img.qammunity.org/2023/formulas/mathematics/college/40ryds6wvsbt0lbi3bg4yn7xygw4qnwj4w.png)
![\text{ 12x - 23 = 4x }+\text{ 17}](https://img.qammunity.org/2023/formulas/mathematics/college/q5irkovtzbyoqkdhgp2jpkes77jll1dfax.png)
![\text{ 12x - 4x = 17 + 23}](https://img.qammunity.org/2023/formulas/mathematics/college/rknt5y99z5q2jggtyepxdjmbi34x0ukd8i.png)
![\text{ 8x = 40}](https://img.qammunity.org/2023/formulas/mathematics/college/jhflii3gpkwn6yewp7ft48h98jpfycouz5.png)
![\text{ }\frac{\text{8x}}{8}\text{ = }\frac{\text{40}}{8}](https://img.qammunity.org/2023/formulas/mathematics/college/h03b0x6ittjxgluzev6kkdl71bjy6y17td.png)
![\text{ x = 5}](https://img.qammunity.org/2023/formulas/mathematics/college/b1jgvdmmlechiefuhb4o3cr0zs10kj4z78.png)
For the diagonals to be equal, x = 5.
Therefore, for it (parallelogram) to be a square, x should be equals to 5.
Let's check,
AC = 12x - 23 = 12(5) - 23 = 60 - 23 = 37
BD = 4x + 17 = 4(5) + 17 = 20 + 17 = 37