Diagonal length is a line from a left corner to a right in a rectangle or square.
Basically making two triangles.
You use the equation a^2+b^2=c^2
So 45.25^2+25.5^2=x^2
2,047.5625+650.25=x^2
2,697.8125=x^2
Then square root them both
51.9404707=x
And when rounding to the nearest number the diagonal length is 52 inches