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JAMB Mathematics 2011 Paper

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Question : 25

Total: 46

A chord of circle of radius 7cm is 5cm from the centre of the circle.What is the length of the chord?

4√6 cm
3√6 cm
6√6 cm
2√6 cm

Solution:

From Pythagoras theorem

|OA|2 = |AN|2 + |ON|2

72 = |AN|2 + (5)2

49 = |AN|2 + 25

|AN|2 = 49 - 25 = 24

|AN| =

\sqrt{24}

=

\sqrt{4 \times 6}

= 2√6 cm

|AN| = |NB| (A line drawn from the centre of a circle to a chord, divides the chord into two equal parts)

|AN| + |NB| = |AB|

2√6 + 2√6 = |AB|

|AB| = 4√6 cm

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