Question 1086004
Your question should be more clearly stated.

I assume you mean a "Right triangle" and you are looking for the hypotenuse.  If so, then you simply need to take the square root of 25/100.

If h is the hypotenuse and a, b are the other two sides:
   {{{ h^2 = a^2 + b^2 }}}
  {{{ h = sqrt(a^2 + b^2) }}} 
   {{{  h = sqrt((3/10)^2 + (4/10)^2) = sqrt(9/100 + 16/100) = sqrt(25/100) = 5/10 }}}