Question 1209956
Maybe "triangle" instead of "trapezoid".


EAch of the equal length legs is d, and hypotenuse is 7.
{{{d^2+d^2=7^2}}}

{{{2d^2=7^2}}}

{{{d^2=7^2/2}}}

{{{d=7/sqrt(2)}}} and you can rationalize denominator if you need.