- Interpret the region
The region is
A={(x,y):x2≤y≤min{x+2,4−3x}}.
So for each fixed x, the upper boundary is the smaller of the two lines:
- y=x+2
- y=4−3x
and the lower boundary is the parabola
Thus the vertical thickness is
min{x+2,4−3x}−x2,
but only where this is nonnegative.
- Find which line is the minimum
We compare the two lines:
x+2=4−3x
4x=2⟹x=21.
Hence:
- for x≤21, we have x+2≤4−3x, so the minimum is x+2;
- for x≥21, the minimum is 4−3x.
So the top boundary is piecewise:
y={x+2,4−3x,x≤21,x≥21.
- Find where the region actually exists
We need
x2≤min{x+2,4−3x}.
So solve separately.
(i) For x≤21
Need
x2≤x+2
x2−x−2≤0
(x−2)(x+1)≤0.
This gives
−1≤x≤2.
But in this case also x≤21, so we get
−1≤x≤21.
(ii) For x≥21
Need
x2≤4−3x
x2+3x−4≤0
(x+4)(x−1)≤0.
This gives
−4≤x≤1.
But here also x≥21, so we get
21≤x≤1.
Therefore the full interval is
−1≤x≤1.
- Set up the area integral
So the required area is
Area=∫−11/2[(x+2)−x2]dx+∫1/21[(4−3x)−x2]dx.
That is,
Area=∫−11/2(−x2+x+2)dx+∫1/21(4−3x−x2)dx.
- Evaluate the first integral
I1=∫−11/2(−x2+x+2)dx.
An antiderivative is
−3x3+2x2+2x.
So
I1=[−3x3+2x2+2x]−11/2.
At x=21:
−3(1/2)3+2(1/2)2+2⋅21=−241+81+1=1+242=1213.
At x=−1:
−3(−1)3+2(−1)2+2(−1)=31+21−2=65−2=−67.
Hence
I1=1213−(−67)=1213+1214=1227=49.
- Evaluate the second integral
I2=∫1/21(4−3x−x2)dx.
An antiderivative is
4x−23x2−3x3.
So
I2=[4x−23x2−3x3]1/21.
At x=1:
4−23−31=624−9−2=613.
At x=21:
4⋅21−23(1/2)2−3(1/2)3=2−83−241=2−2410=2−125=1219.
Hence
I2=613−1219=1226−19=127.
- Total area
Area=I1+I2=49+127=1227+127=1234=617.
- Match with options
617
corresponds to Option B.
- Comparison with stored answer
Stored correct answer: B
Our derived answer: B
So they agree.