# I have 2 concentric circles and a tangent, can you help me find the surface area?

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By Pythag in this triangle, R^2 – r^2 = [11.5]^2

you don,t need to find R, in fact you can`t, but the area you need is given by:

A = pi[R^2 – r^2]

= pi[11.5]^2, and I`m sure that you can work this out ? Hope this helps, Twiggy

If, for example, the radius of the inner circle were known to be r, then you could join the point of contact of the tangent to the centre of the circles, and join the centre to the two extremities of the tangent.

That would give you two right-angled triangles, each with one side equal to 23/2 and the other equal to r.

Then you could use Pythagoras’ theorem to find the radius of the larger circle, which would be the hypotenuse. With that, you could calculate the area.

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