CBSE Class 9 Answered

drop perpendiculars from the center O to the chords, naturally these perpendiculars have to meet the chords at their mid points.

let M and N be the mid points of the chords AB,CD respectively.

since the chords are parallel, so MON is a straight line.

let MO= x then NO=7-x... since the dist between the chords is given as 7 cm.

consider triangles OMB,

MB=3

OM=x

consider triangle OND,

ND=4

ON=7-x

if  r is the radius, then, by Pythagoras' theorem we get

solving we get,

x=4

so

 r=5