Question Details

For real values of x, the range of the function f(x) = 2x3 2 x2 + 4x 6    is

Options

A

( , 18 ] [ 1 , )

B

( , 14 ] [ 1 , )

C

( , 18 ] [ 12 , )

D

( , 14 ] [ 12 , )

Show Answer

Correct Answer :

Option C

( , 18 ] [ 12 , )

Solution :

The correct option is:
( , 1 8 ] [ 1 2 , )

Step-by-Step Explanation:

Let the given function be represented by y:
y = 2 x 3 2 x 2 + 4 x 6

First, we note that the domain of the function excludes values of x that make the denominator zero.
The denominator is:
2 x 2 + 4 x 6 = 2 ( x + 3 ) ( x 1 )
Thus, the domain of the function is all real numbers x except x = 1 and x = 3 .

Now, we rewrite the equation by cross-multiplying:
y ( 2 x 2 + 4 x 6 ) = 2 x 3
Expanding and rearranging the terms to form a quadratic equation in terms of x:
2 y x 2 + 4 y x 6 y = 2 x 3
2 y x 2 + ( 4 y 2 ) x + ( 3 6 y ) = 0

For x to be a real number, the discriminant D of this quadratic equation must be greater than or equal to zero (assuming y 0 ).
The discriminant D is given by:
D = b 2 4 a c 0
Here, a = 2 y , b = 4 y 2 , and c = 3 6 y . Substituting these values:
( 4 y 2 ) 2 4 ( 2 y ) ( 3 6 y ) 0

Let's simplify the inequality step-by-step:
Factor out 2 from the term ( 4 y 2 ) , which gives 2 2 ( 2 y 1 ) 2 = 4 ( 2 y 1 ) 2 .
Substitute this back:
4 ( 2 y 1 ) 2 8 y ( 3 6 y ) 0
Divide the entire inequality by 4:
( 2 y 1 ) 2 2 y ( 3 6 y ) 0
Expand the terms:
( 4 y 2 4 y + 1 ) 6 y + 12 y 2 0
Combine like terms:
16 y 2 10 y + 1 0

Now, we factor the quadratic expression:
16 y 2 8 y 2 y + 1 0
8 y ( 2 y 1 ) 1 ( 2 y 1 ) 0
( 8 y 1 ) ( 2 y 1 ) 0

Solving this quadratic inequality yields:
y 1 8  or  y 1 2

Finally, we check if the boundary values are attainable by substituting them back into the quadratic equation in x:
If y = 1 8 , the equation becomes:
2 ( 1 8 ) x 2 + [ 4 ( 1 8 ) 2 ] x + [ 3 6 ( 1 8 ) ] = 0
1 4 x 2 3 2 x + 9 4 = 0 x 2 6 x + 9 = 0 ( x 3 ) 2 = 0 x = 3
Since x = 3 is a valid real number in the domain, y = 1 8 is attainable.

If y = 1 2 , the equation becomes:
2 ( 1 2 ) x 2 + [ 4 ( 1 2 ) 2 ] x + [ 3 6 ( 1 2 ) ] = 0
x 2 + 0 x + 0 = 0 x = 0
Since x = 0 is a valid real number in the domain, y = 1 2 is also attainable.

Thus, the range of the function is:
y ( , 1 8 ] [ 1 2 , )

Unlock Our Free Library

Access expert-curated educational resources and study materials—completely free.

Discover more resources

You may also like

Mock Tests

View All
  • CTET
  • intermediate
  • No time limit
  • child development and pedagogy, mathematics, social science

  • SSC
  • intermediate
  • 2 hours and 30 mins
  • child development and pedagogy, mathematics, social science

Ask AI Tutor
5 left
Q1 View Question & Options
AI Tutor is solving this question...
Reading question context & options...