Question 1066460
Think from what the 30-60-90 special triangle comes from.  Or draw it.  The altitude of equilateral triangle cuts into two right triangles each congruent, of this 30-60-90 special right triangle type.


The short leg length is half the hypotenuse length.  If your short leg is x, and your hypotenuse is y, then  you have  {{{y/2=x}}}.


As for getting the actual value of either x or y,  you should know what to do using the Pythagorean Theorem formula for right triangle.  
{{{(longLeg)^2+(shortLeg)^2=hypotenuse^2}}}
{{{(10sqrt(3))^2+x^2=(2x)^2}}}
{{{300+x^2=4x^2}}}
{{{3x^2=300}}}
{{{x^2=100}}}
{{{highlight(x=10)}}}


Short leg, {{{x=10}}};
hypotenuse, {{{y=2*x=20}}}.