Three horses are tethered with 7 cm long ropes at the three comers of a triangular field having sides 20 m, 34 m and 42 m. Find the area of the plot which can be grazed by the horses. Also, find the area of the point which remains ungrazed.

Clearly, let
∠A = ө₁, ∠B = ө₂ ∠C = ө₃

We have,
r = 7 m,
a = 34 m, b = 42 m, c= 20 m
Now, area which can be grazed by the horses = Sum of the areas of three sectors with central angles ө₁, ө₂ and ө₃ each with radius (r) = 7 m

Now, we can find out area of the triangle by using Heron's formula.
Here, we have

Angle described by the minute hand in 60 minutes = 360°.
Angle described by the minute hand in 35 minutes

         
Thus, we have,

              = 210, and r = 12 cm.
Therefore, required area