Question 885401
Special triangle, half of an equilateral triangle.  If x is the length of the short side of the 30-60-90 triangle, then the long side is the hypotenuse of 2x.  The other side is your given middle side of 9 units.


{{{(1/2)x*9}}} is area; and {{{(2x)^2=9^2+x^2}}} using Pythagorean Theorem for the Right Triangle.