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Solutions
The tangents drawn to a circle from a point are of equal lengths.
Hence EC = EF = 4 cm.
AD = AF = 6 cm.
Let DB = BE = kcm.
The lengths of the sides of the triangle are AB = 6+k.
BC = 4+k cm.
AC = 10 cm.
Applying cosine rule for angle ACB
$$Cos\alpha\ \ =\ \frac{\left(b^2+c^2-a^2\right)}{2\cdot b\cdot c}$$.
Now looking at the sides b =k+4, c = 10cm, and a = k+6 cm.
Cos(60) = $$\frac{\left(\left(\left(k+4\right)^2\right)+100-\left(k+6\right)^2\right)}{2\cdot\left(k+4\right)\left(10\right)}$$
Solving this we get
10k + 40 = $$k^2+8k+16+100-\left(k^2+12k+36\right)$$
k = 20/7 cm.
Now the sides are 4+k = 48/7 cm, 10 cm, 6+k = 62/7 cm.
The circum radius of the triangle is given by
R = abc/4(Area of the triangle)
R = $$\frac{abc}{4\cdot\left(\frac{1}{2}a\cdot b\cdot SinC\right)}$$
= c/2Sin(C)
c = 62/7 cm, Sin(C) = $$\frac{\sqrt{\ 3}}{2}$$
$$\frac{62}{7\sqrt{\ 3}}\ =\ \frac{62\sqrt{\ 3}}{21}$$ cm