You may also like

problem icon

Baby Circle

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?

problem icon

Ab Surd Ity

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

problem icon

Absurdity Again

What is the value of the integers a and b where sqrt(8-4sqrt3) = sqrt a - sqrt b?

Irrational Arithmagons

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

In a multiplication arithmagon, the number on each edge of the arithmagon is the product of the numbers at the adjacent vertices.

You may wish to look at Multiplication Arithmagons and develop a general strategy for working out the numbers at the vertices, given the edge numbers, before tackling the question below.

 
Can you work out the numbers that belong in the circles to make this multiplication arithmagon correct?
arithmagon with -6 + 2 root 2, 7 + 7 root 2, 2 - 4 root 2

 
 If you're not sure where to start, click for a series of hints:

Each circle will be of the form $a+b\sqrt2$ for some values of $a$ and $b$. 
 
In general, a multiplication arithmagon can be solved by multiplying, dividing, and square-rooting.
 
Dividing an expression by $a+b\sqrt2$ is the same as saying, "What must I multiply $a+b\sqrt2$ by to get that expression?"
 
To find the square root of an expression such as $12-8\sqrt2$, consider the equation $(x+y\sqrt2)^2=12-8\sqrt2$, expand the brackets, and deduce $x$ and $y$.