Question

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Answer 1

https://www.desmos.com/calculator/zxsaiyz5di

Answer 2

you can use the distance formula
(from (-1,3) to (1-,3) and that will give you the diagonal length)

Answer 3

Or, if you are familiar with a 45-45-90 triangle well enough, then you can find the length and width of rectangle and then use the Pythagorean Theorem.

Answer 4

Distance formula:
\(\Large\color{black}{ \displaystyle {\rm D} =\sqrt{ (\color{blue}{{\rm y}_1}-\color{red}{{\rm y}_2})^2+(\color{green}{{\rm x}_1}-\color{darkgoldenrod}{{\rm x}_2})^2 }}\)


where
\(\Large\color{black}{ \displaystyle {\rm D} }\) is the distance.

\(\Large\color{black}{ \displaystyle (\color{green}{{\rm x}_1}~,~~\color{blue}{{\rm y}_1}) }\) and \(\Large\color{black}{ \displaystyle (\color{darkgoldenrod}{{\rm x}_2}~,~~\color{red}{{\rm y}_2}) }\) are your two points.