Two semicircles, a tangent and an altitude to the tangency point. Prove that the red triangle is isosceles.
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Solution

Poem
The dolphin
Is fast moving and speedy
He can hear very well and
feeds largely
Dolphin mothers care for calves with responsability
They vocalyze and wistle usually
And can be a comfort when sadness, for you and me
Some say, if you wish
The dolphin is the king of the fish
