Question

The area of the region bounded by the curves $y_1(x) = x^4 - 2x^2$ and $y_2(x) = 2x^2$, $x \in \mathbb{R}$, is
 

• A. $\dfrac{128}{15}$
• B. $\dfrac{129}{15}$
• C. $\dfrac{133}{15}$
• D. $\dfrac{134}{15}$

Hint:

To find the area between two curves, always subtract the lower curve from the upper one and integrate within the intersection limits.

Answer 1

The Correct Option is A

Step 1: Points of intersection. 
To find the intersection points, set $y_1 = y_2$: \[ x^4 - 2x^2 = 2x^2 $\Rightarrow$ x^4 - 4x^2 = 0 $\Rightarrow$ x^2(x^2 - 4) = 0. \] Hence, $x = 0, \pm 2$. 
 

Step 2: Area between curves. 
The required area is \[ A = 2 \int_0^2 [(2x^2) - (x^4 - 2x^2)] dx = 2 \int_0^2 (4x^2 - x^4) dx. \]

Step 3: Integration. 
\[ A = 2 \left[\frac{4x^3}{3} - \frac{x^5}{5}\right]_0^2 = 2 \left[\frac{32}{3} - \frac{32}{5}\right]. \] \[ A = 2 \times \frac{160 - 96}{15} = \frac{128}{15}. \]
 

Step 4: Conclusion. 
Hence, the area of the region bounded by the given curves is $\dfrac{128}{15}$.