From the figure, it can be observed that the horse can graze a sector of 90° in a circle of 5 m radius.
Area that can be grazed by horse
= Area of sector OACB
Area that can be grazed by the horse when length of rope is 10 m long
Increase in grazing area = (78.5 − 19.625) m2 = 58.875 m2