1+1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9=? ?=x*x
It looks like ? = 2 * 9 triangulated
x triangulated = (x2 + x)/2
? = 92+9
? = 90
? = x2
90 = x2
\(x =3\sqrt{10}\)
+633 
