In the figure given below, find the distance PQ.
Explanation:
BC2 = AB2 + AC2 = 152 + 202 = 625
BC = 25
Let BD = x, so DC = 25 − x
In ΔABD,
BD2 + AD2 = AB2
x2 + AD2 = 225 ... (i)
In ΔADC,
AD2 + (25 − x)2 = 400
∴ AD2 + 625 − 50x + x2 = 400
∴ (AD2 + x2) + 625 − 50x = 400 ... (ii)
Substituting (i) in (ii),
225 + 625 − 50x = 400
∴ x = 9
BD = 9 and DC = 16
We use the formula A = r × S, where A is the area of a triangle, r is the inradius and S is the semi-perimeter to find the radii of the two circles.
The radius of the circle inscribed in ∆ABD = 3 m
The radius of the circle inscribed in ∆ADC = 4 m
∴ PQ = radius of ∆ABC + radius of ∆ADC = 7 m
Hence, option (a).
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