Can someone help me I'm lost

Answer: [tex]\sqrt{6}[/tex]
This is the same as typing in sqrt(6)
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Explanation:
The square has all four sides the same length, which in this case is [tex]\sqrt{3}[/tex] units.
The diagonal of the square splits it into two identical right triangles.
Use the Pythagorean Theorem to find the hypotenuse x, aka the diagonal.
[tex]a^2 + b^2 = c^2\\\\c = \sqrt{a^2 + b^2}\\\\x = \sqrt{\left(\sqrt{3}\right)^2+\left(\sqrt{3}\right)^2}\\\\x = \sqrt{3+3}\\\\x = \sqrt{6}\\\\[/tex]
Or you can take the shortcut
[tex]\text{hypotenuse} = (\text{leg})*\sqrt{2}\\\\x = \sqrt{3}*\sqrt{2}\\\\x = \sqrt{3*2}\\\\x = \sqrt{6}\\\\[/tex]
Which applies to 45-45-90 right triangles.
let's recall that a square has four equal sides, Check the picture below.