In a rectangle, the diagonals are equal in length. Therefore, we can set the two expressions for the diagonals equal to each other:
\[ x + 7 = 3x - 5 \]
Now, let's solve for \(x\):
- Subtract \(x\) from both sides:
\[ 7 = 3x - x - 5 \]
which simplifies to:
\[ 7 = 2x - 5 \]
- Next, add 5 to both sides:
\[ 7 + 5 = 2x \]
which simplifies to:
\[ 12 = 2x \]
- Now, divide both sides by 2:
\[ x = 6 \]
Thus, the value of \(x\) that makes ABCD a rectangle is:
x = 6.