Find the length of a chord which is at a distance of 9 cm from the centre of a circle of radius 15 cm.
Given radius(AO) = 15cm
Length of the chord (AB) = x
distance of the chord from the centre is 9cm.
Draw a perpendicular bisector from center to the chord and name it OC.
AC = BC
Now in ∆ AOC
Using Pythagoras theorem
AO2 = AC2 + OC2
152 = AC2 + 92
AC2 = 152 – 92
AC2 = 225 – 81
AC2 = 144
AC = 12cm
BC = 12cm
The length of the chord is AC + BC = 12 + 12 = 24 cm.