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'Partly Circles' printed from

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Here are three problems involving circles.

Can you solve them?
Can you find relationships between the three problems?

Firstly :
Show that ab = cd
            (where a, b, c, d are lengths)


These three circles are drawn so that they touch each other, and their centres are all on the line AB.

If CD is $8$ units in length, what is the area of the region shaded yellow?


If the area shaded yellow is equal to the area of the larger of the two blue circles, what is the relationship between the radii of the three circles?