Question 86794
---Step#1:  Draw the triangle and the height
you will notice you have equal-lateral triangle, something like the below
{{{ graph( 300, 200, -5, 5, 0, 5, 4x+5, -4x+5) }}}
Where the slant sides are 13 and the base is 10
use {{{a^2 + b^2 = c^2 }}}
where "c" is your slant side
"b" is your height or altitude
"a" is the base.....remember "a" is 5 (half the 10)