Question 136132
You will have to draw yourself a picture of what is going on here, but the total grazing area is going to be 3/4 of a circle with a radius of 18 feet, plus and additional half (two quarters) of a circle with a radius of 8 feet.


Imagine the horse is standing on a line that is the extension of one side of the square corral.  He can go anywhere within the 18 foot radius circle centered at the point he is tethered, except for that quarter of the circle enclosed in the corral itself.  That's where I get 3/4 of an 18' circle.


But he can also continue around the corner of the corral 10' from where he is tethered.  The rope will wrap around the corner of the corral, and he will have 8 feet of rope (18 - 10) left to cover the quarter circle bounded by the extension of the side of the square and the adjacent side of the square.  There are two such quarter circles.


So:  {{{(3*pi*18^2)/4 + (pi*8^2)/2}}}


You do the arithmetic