Question Details

The set of all real values of x for which  ( x 2 | x + 9 | + x ) > 0 , is

Options

A

( , 3 ) ( 3 , )

B

( , 9 ) ( 3 , )

C

( 9 , 3 ) ( 3 , )

D

( , 9 ) ( 9 , )

Show Answer

Correct Answer :

Option A

( , 3 ) ( 3 , )

Solution :

The correct option is:
( , 3 ) ( 3 , )

To solve the given inequality, we must eliminate the absolute value. The inequality is:

x 2 | x + 9 | + x > 0

The expression inside the absolute value is x+9. Since the absolute value function behaves differently depending on whether its argument is positive or negative, we must split the problem into two distinct cases: when x+90 and when x+9<0.

Case 1: x + 9 0

This condition implies that:
x 9
Since x+9 is non-negative, the absolute value is simply the expression itself: |x+9|=x+9. Substituting this back into our original inequality gives:

x 2 ( x + 9 ) + x > 0

Now, distribute the negative sign and simplify:

x 2 x 9 + x > 0
x 2 9 > 0
x 2 > 9

Taking the square root of both sides, we get:
x < 3  or  x > 3

However, we must also satisfy our Case 1 condition, x9. By intersecting these requirements, the valid interval for Case 1 is:
x [ 9 , 3 ) ( 3 , )

Case 2: x + 9 < 0

This condition implies that:
x < 9
Since x+9 is negative in this case, its absolute value is its negation: |x+9|=(x+9). Substitute this back into the original inequality:

x 2 ( ( x + 9 ) ) + x > 0

This simplifies to:

x 2 + x + 9 + x > 0
x 2 + 2 x + 9 > 0

Let's analyze the quadratic equation x2+2x+9 by checking its discriminant (D=b24ac):
D = 2 2 4 ( 1 ) ( 9 ) = 4 36 = 32

Because the discriminant is negative (D<0) and the leading coefficient (x2) is positive, the quadratic expression x2+2x+9 is strictly greater than 0 for all real numbers x.
Thus, the inequality holds true for any value in Case 2. The valid interval here is strictly determined by our case condition:
x ( , 9 )

Combining the Cases

The total solution is the union of the valid intervals from Case 1 and Case 2:
x ( , 9 ) [ 9 , 3 ) ( 3 , )

Notice how the boundary 9 perfectly joins the first two sets, simplifying the expression to:

x ( , 3 ) ( 3 , )

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