27.The radii of two concentric circles are 13cm and 8 cm. AB is a diam

1.	27.The radii of two concentric circles are 13cm and 8 cm. AB is a diameter of the biggercircte. BD is a tangent to the smaller circletouching it at D. Find the length AD.
Answer» To know AD,we need to know AC & CD. To findthem, we need BC and BD first. Given OA=OB = R ,OD= r Let theradii of circles be R & r. R > r.R= 13cm r = 8cm. Finally: AD =√(R²+3 r²) =√(13²+3*8²) = 19 cm

27.The radii of two concentric circles are 13cm and 8 cm. AB is a diameter of the biggercircte. BD is a tangent to the smaller circletouching it at D. Find the length AD.

Answer»

To know AD,we need to know AC & CD.

To findthem, we need BC and BD first.

Given OA=OB = R ,OD= r

Let theradii of circles be R & r. R > r.R= 13cm r = 8cm.

Finally: AD =√(R²+3 r²) =√(13²+3*8²) = 19 cm