Points A, B and C are the centres of three circles, each one of
which touches the other two. Prove that the perimeter of the
triangle ABC is equal to the diameter of the largest circle.
Weekly Problem 37 - 2013
The diagram shows two semicircular arcs... What is the diameter of the shaded region?
Congratulations to Matthew Hodgetts, King Edward VI Camp Hill
School, Birmingham, to Suzanne Abbott, Nisha Doshi and Christiane
Eaves, Mount School, York; to Jessica Zhang; to the KS3 Maths Club,
Strabane Grammar School and finally to Michael Swarbrick-Jones, Y7
Comberton Village College, Cambridge whose solution appears
x = the diameter of one of the circles.
Since (AC) and (BD) are both the length of a radius then x
= (AC) + (BD).
So x = 12 - (AB) = 12 - x/3.
So x + x/3 = 12
or 4/3 x = 12.
To find x we take the reciprocal of 4/3 and multiply it
x = 9 units.