A parabola is tangent to the circle at and as shown above.
If the area of the region bounded by the parabola and the circle above can be represented as , where and are coprime positive integers, find .
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m O A = 3 1 ⟹ m ⊥ = − 3
m O B = − 3 1 ⟹ m ⊥ ∗ = 3
Let y = a x 2 + b x + c ⟹ d x d y = 2 a x + b
⟹ d x d y ∣ ( x = 2 3 ) = 3 a + b = − 3
and
d x d y ∣ ( x = 2 − 3 ) = − 3 a + b = 3
Solving the above system we obtain a = − 1 and b = 0 and using A ( 2 3 , 2 1 ) ⟹
2 1 = − 1 ( 2 3 ) 2 + c ⟹ c = 4 5 ⟹ y = 4 5 − x 2
and for the portion of the circle we have y = 1 − x 2
⟹ A = 2 ∫ 0 2 3 ( ( 4 5 − x 2 ) − 1 − x 2 ) d x
= 2 ( 2 3 − ∫ 0 2 3 1 − x 2 d x )
Letting x = sin ( θ ) ⟹ d x = cos ( θ ) d θ ⟹
∫ 0 2 3 1 − x 2 d x = ∫ 0 3 π ( 1 + cos ( 2 θ ) ) d θ = 2 1 ( θ + 2 1 sin ( 2 θ ) ) ∣ 0 3 π =
2 1 ( 3 π + 4 3 )
⟹ A = 3 − ( 3 π + 4 3 ) = 4 3 3 − 3 π = b a a − a π ⟹ a + b = 7 .