A chord AB of a circle is at a distance of 6cm from the centre of a circle whose radius is 6cm less than the chord AB. Find the length of the chord and radius of the circle
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let the length of the cord be x cm and the perpendicular from the centre to the cord be OP
so AP =x/2 (since perpendicular from centre to cord bisects the cord )
in rt triangle OPA
OA2= AP2+ OP2
i.e. (x-6)2= (x/2)2+ 62
x2-12x +36 = x2/4 +36
implies x2-12x =x2 /4
4x2-48x = x2
3x2-48x = 0
x2 -16x = 0
x2 = 16x
x2/x =16
x= 16cm
therefore the length of the cord is 16cm and the radius is 10 cm
so AP =x/2 (since perpendicular from centre to cord bisects the cord )
in rt triangle OPA
OA2= AP2+ OP2
i.e. (x-6)2= (x/2)2+ 62
x2-12x +36 = x2/4 +36
implies x2-12x =x2 /4
4x2-48x = x2
3x2-48x = 0
x2 -16x = 0
x2 = 16x
x2/x =16
x= 16cm
therefore the length of the cord is 16cm and the radius is 10 cm
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