A chord 21 cm long is drawn in a circle of diameter 25 cm. The perpendicular distance of the chord from the centre is:

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SSC CGL 2020 Tier-I Official Paper 1 (Held On : 13 Aug 2021 Shift 1)
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  1. √41
  2. √23
  3. √56
  4. √46

Answer (Detailed Solution Below)

Option 4 : √46
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Detailed Solution

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F1 Ashish Madhu 19.10.21 D3

Given:

Chord = 21cm 

Diameter = 25 cm 

Concept:

The perpendicular drawn from the center on the chord, bisects the chord in two equal parts. 

Pythagoras Theorem:

OA2 = OD2 + AD2

Calculation:

Let AB be the chord of length 21 cm. 

⇒ OD be the perpendicular distance 

⇒ AO be the radius of the circle 

OA2 = OD2 + AD2

⇒ (25/2)2 = OD2 + (21/2)2

⇒ 625/4 = OD2 + 441/4 

⇒ OD2 = 625/4 - 441/4 = 184/4 = 46 

∴ OD = √46 

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