Q43 / 90 · NTA Abhyas (JEE Main) 2020 · Mathematics · Area Under Curves

The area between the curve y=2x4-x2, the x-axis and the ordinates of the two minima of the curve is

  • A
    11 60  sq. units 
  • Correct answer
    B
    7 120  sq. units
  • C
    1 30  sq. units
  • D
    7 90  sq. units

Solution

The equation of the curve is y=2x4-x2=2x2-1 x 2

The curve is symmetrical about the y -axis.

Also, it is a polynomial of degree four having roots 0, 0, ± 1 2 .

x=0 is repeated root. Hence, graph touches x -axis at (0,0) and intersects the x -axis at A − 1 2 ,  0  & B 1 2 ,  0

⇒ dy dx =8 x 3 −2x

=2x(4 x 2 −1)=0

x=0, x=± 1 2

d 2 y d x 2 >0 at x= 1 2 and at x= −1 2

So x = ± 1 2 are the points of local minima

Thus, the graph of the curve is shown in diagram.

Figure

Here, y≤0 , as x varies from x=-12 to x=12

∴ The required area

=2 Area OCDO

=2∫012y dx

=2∫0122x4-x2 dx

=7120 sq. units

Hence, the correct answer is option: 'B'.

More Area Under Curves Questions