Second Epsilons

This is our second collection of stage 5 epsilons. An epsilon problem is quick to read and understand. They might not be so easy to solve!

Epsilons will be good for filling spare mathematical moments. Why not carry a few around with you? (Our first collection of epsilons are here).

Baby Circle

Stage: 5 Challenge Level: Challenge Level:1

A small circle fits between two touching circles so that all three circles touch each other and have a common tangent? What is the exact radius of the smallest circle?

Upsetting Pitagoras

Stage: 4 and 5 Challenge Level: Challenge Level:2 Challenge Level:2

Find the smallest integer solution to the equation 1/x^2 + 1/y^2 = 1/z^2

Ab Surd Ity

Stage: 5 Challenge Level: Challenge Level:1

Find the value of sqrt(2+sqrt3)-sqrt(2-sqrt3)and then of cuberoot(2+sqrt5)+cuberoot(2-sqrt5).

BT.. Eat Your Heart Out

Stage: 5 Challenge Level: Challenge Level:2 Challenge Level:2

If the last four digits of my phone number are placed in front of the remaining three you get one more than twice my number! What is it?

Biggest Bendy

Stage: 5 Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3

Four rods are hinged at their ends to form a quadrilateral with fixed side lengths. Show that the quadrilateral has a maximum area when it is cyclic.

Three Ways

Stage: 5 Challenge Level: Challenge Level:1

If x + y = -1 find the largest value of xy by coordinate geometry, by calculus and by algebra.