Given region
We need the area of
{ ( x , y ) : ∣ 4 − x 2 ∣ ≤ y ≤ x 2 , y ≤ 4 , x ≥ 0 } . \{(x,y): |4-x^2|\le y\le x^2,\ y\le 4,\ x\ge 0\}. {( x , y ) : ∣4 − x 2 ∣ ≤ y ≤ x 2 , y ≤ 4 , x ≥ 0 } .
So for each x ≥ 0 x\ge 0 x ≥ 0 , the allowed y y y must satisfy:
lower bound: y ≥ ∣ 4 − x 2 ∣ y\ge |4-x^2| y ≥ ∣4 − x 2 ∣
upper bounds: y ≤ x 2 y\le x^2 y ≤ x 2 and y ≤ 4 y\le 4 y ≤ 4
Hence the actual upper bound is
y ≤ min ( x 2 , 4 ) . y\le \min(x^2,4). y ≤ min ( x 2 , 4 ) .
So the vertical strip exists when
∣ 4 − x 2 ∣ ≤ min ( x 2 , 4 ) . |4-x^2|\le \min(x^2,4). ∣4 − x 2 ∣ ≤ min ( x 2 , 4 ) .
Split according to x x x
Because of x 2 x^2 x 2 and 4 4 4 , the natural breakpoints are around x = 2 x=2 x = 2 .
Case 1: 0 ≤ x ≤ 2 0\le x\le 2 0 ≤ x ≤ 2
Then x 2 ≤ 4 x^2\le 4 x 2 ≤ 4 , so
min ( x 2 , 4 ) = x 2 . \min(x^2,4)=x^2. min ( x 2 , 4 ) = x 2 .
Also,
∣ 4 − x 2 ∣ = 4 − x 2 |4-x^2|=4-x^2 ∣4 − x 2 ∣ = 4 − x 2
since x 2 ≤ 4 x^2\le 4 x 2 ≤ 4 .
Thus the strip is
4 − x 2 ≤ y ≤ x 2 . 4-x^2\le y\le x^2. 4 − x 2 ≤ y ≤ x 2 .
This is possible only if
4 − x 2 ≤ x 2 ⟹ 4 ≤ 2 x 2 ⟹ x 2 ≥ 2 ⟹ x ≥ 2 . 4-x^2\le x^2
\implies 4\le 2x^2
\implies x^2\ge 2
\implies x\ge \sqrt{2}. 4 − x 2 ≤ x 2 ⟹ 4 ≤ 2 x 2 ⟹ x 2 ≥ 2 ⟹ x ≥ 2 .
So in this range, valid x x x are
2 ≤ x ≤ 2. \sqrt{2}\le x\le 2. 2 ≤ x ≤ 2.
The height of the strip is
x 2 − ( 4 − x 2 ) = 2 x 2 − 4. x^2-(4-x^2)=2x^2-4. x 2 − ( 4 − x 2 ) = 2 x 2 − 4.
Case 2: x ≥ 2 x\ge 2 x ≥ 2
Then x 2 ≥ 4 x^2\ge 4 x 2 ≥ 4 , so
min ( x 2 , 4 ) = 4. \min(x^2,4)=4. min ( x 2 , 4 ) = 4.
Also,
∣ 4 − x 2 ∣ = x 2 − 4. |4-x^2|=x^2-4. ∣4 − x 2 ∣ = x 2 − 4.
Thus the strip is
x 2 − 4 ≤ y ≤ 4. x^2-4\le y\le 4. x 2 − 4 ≤ y ≤ 4.
This is possible only if
x 2 − 4 ≤ 4 ⟹ x 2 ≤ 8 ⟹ x ≤ 2 2 . x^2-4\le 4
\implies x^2\le 8
\implies x\le 2\sqrt{2}. x 2 − 4 ≤ 4 ⟹ x 2 ≤ 8 ⟹ x ≤ 2 2 .
So in this range, valid x x x are
2 ≤ x ≤ 2 2 . 2\le x\le 2\sqrt{2}. 2 ≤ x ≤ 2 2 .
The height of the strip is
4 − ( x 2 − 4 ) = 8 − x 2 . 4-(x^2-4)=8-x^2. 4 − ( x 2 − 4 ) = 8 − x 2 .
Set up the area integral
Therefore,
A = ∫ 2 2 ( 2 x 2 − 4 ) d x + ∫ 2 2 2 ( 8 − x 2 ) d x . A=\int_{\sqrt{2}}^{2}(2x^2-4)\,dx+\int_{2}^{2\sqrt{2}}(8-x^2)\,dx. A = ∫ 2 2 ( 2 x 2 − 4 ) d x + ∫ 2 2 2 ( 8 − x 2 ) d x .
Evaluate the first integral
∫ ( 2 x 2 − 4 ) d x = 2 x 3 3 − 4 x . \int (2x^2-4)dx=\frac{2x^3}{3}-4x. ∫ ( 2 x 2 − 4 ) d x = 3 2 x 3 − 4 x .
So
∫ 2 2 ( 2 x 2 − 4 ) d x = [ 2 x 3 3 − 4 x ] 2 2 . \int_{\sqrt{2}}^{2}(2x^2-4)dx
=\left[\frac{2x^3}{3}-4x\right]_{\sqrt{2}}^{2}. ∫ 2 2 ( 2 x 2 − 4 ) d x = [ 3 2 x 3 − 4 x ] 2 2 .
At x = 2 x=2 x = 2 :
2 ( 8 ) 3 − 8 = 16 3 − 8 = − 8 3 . \frac{2(8)}{3}-8=\frac{16}{3}-8=-\frac{8}{3}. 3 2 ( 8 ) − 8 = 3 16 − 8 = − 3 8 .
At x = 2 x=\sqrt{2} x = 2 :
2 ( 2 ) 3 3 − 4 2 = 2 ( 2 2 ) 3 − 4 2 = 4 2 3 − 4 2 = − 8 2 3 . \frac{2(\sqrt{2})^3}{3}-4\sqrt{2}
=\frac{2(2\sqrt{2})}{3}-4\sqrt{2}
=\frac{4\sqrt{2}}{3}-4\sqrt{2}
=-\frac{8\sqrt{2}}{3}. 3 2 ( 2 ) 3 − 4 2 = 3 2 ( 2 2 ) − 4 2 = 3 4 2 − 4 2 = − 3 8 2 .
Therefore,
I 1 = − 8 3 − ( − 8 2 3 ) = 8 2 − 8 3 . I_1=-\frac{8}{3}-\left(-\frac{8\sqrt{2}}{3}\right)
=\frac{8\sqrt{2}-8}{3}. I 1 = − 3 8 − ( − 3 8 2 ) = 3 8 2 − 8 .
Evaluate the second integral
∫ ( 8 − x 2 ) d x = 8 x − x 3 3 . \int (8-x^2)dx=8x-\frac{x^3}{3}. ∫ ( 8 − x 2 ) d x = 8 x − 3 x 3 .
So
∫ 2 2 2 ( 8 − x 2 ) d x = [ 8 x − x 3 3 ] 2 2 2 . \int_{2}^{2\sqrt{2}}(8-x^2)dx
=\left[8x-\frac{x^3}{3}\right]_{2}^{2\sqrt{2}}. ∫ 2 2 2 ( 8 − x 2 ) d x = [ 8 x − 3 x 3 ] 2 2 2 .
At x = 2 2 x=2\sqrt{2} x = 2 2 :
8 ( 2 2 ) − ( 2 2 ) 3 3 = 16 2 − 16 2 3 = 32 2 3 . 8(2\sqrt{2})-\frac{(2\sqrt{2})^3}{3}
=16\sqrt{2}-\frac{16\sqrt{2}}{3}
=\frac{32\sqrt{2}}{3}. 8 ( 2 2 ) − 3 ( 2 2 ) 3 = 16 2 − 3 16 2 = 3 32 2 .
At x = 2 x=2 x = 2 :
16 − 8 3 = 40 3 . 16-\frac{8}{3}=\frac{40}{3}. 16 − 3 8 = 3 40 .
Therefore,
I 2 = 32 2 3 − 40 3 . I_2=\frac{32\sqrt{2}}{3}-\frac{40}{3}. I 2 = 3 32 2 − 3 40 .
Total area
A = I 1 + I 2 = 8 2 − 8 3 + 32 2 − 40 3 = 40 2 − 48 3 . A=I_1+I_2
=\frac{8\sqrt{2}-8}{3}+\frac{32\sqrt{2}-40}{3}
=\frac{40\sqrt{2}-48}{3}. A = I 1 + I 2 = 3 8 2 − 8 + 3 32 2 − 40 = 3 40 2 − 48 .
So
A = 40 2 3 − 16. A=\frac{40\sqrt{2}}{3}-16. A = 3 40 2 − 16.
This matches the form
80 2 α − β . \frac{80\sqrt{2}}{\alpha}-\beta. α 80 2 − β .
Thus,
80 2 α = 40 2 3 ⟹ α = 6 , \frac{80\sqrt{2}}{\alpha}=\frac{40\sqrt{2}}{3}
\implies \alpha=6, α 80 2 = 3 40 2 ⟹ α = 6 ,
and
β = 16. \beta=16. β = 16.
Hence,
α + β = 6 + 16 = 22. \alpha+\beta=6+16=22. α + β = 6 + 16 = 22.
Comparison with stored answer
Derived answer = 22 22 22 .
Stored correct answer = 22 22 22 .
They agree.