In Major League Baseball what is the distance from first base to second?

Approximately 127 feet

All of the bases are 90 feet apart.

So you have a right triangle. To find the hypotenuse of a right triangle you can use the pythagorean theorem: A^2 + B^2 = C^2

90 ^2 + 90 ^2 = C ^2

8100 + 8100 = C^2

The square root of 16200 is 127.27 That measurement is from the tip (back) of home plate to the center of second. Home plate, first and third base are completely within the 90 ft per side square (diamond) that makes up the infield. The center of second base is at the intersection of the 1-2 and 2-3 baselines and therefore partially (well mostly) outside the diamond.