Question Details

If 9 x2 + 2x 3 4 ( 3 x2 + 2x 2 ) + 27 = 0   then the product of all possible values of x is

Options

A

30

B

20

C

5

D

15

Show Answer

Correct Answer :

Option B

20

Solution :

The correct answer is 20.

Let us solve the given exponential equation step-by-step:

9 x2 + 2x 3 4 ( 3 x2 + 2x 2 ) + 27 = 0

First, notice that the exponents share a common structure. Let us define a new variable to simplify the expressions. We can express the exponents in terms of y=x2+2x3. Notice that the exponent in the second term is x2+2x2, which is simply y+1.

Substituting y into our original equation, we obtain:

9y 4 ( 3y+1 ) + 27 = 0

Next, we write the terms with a common base of 3. We know that 9y=(32)y=(3y)2 and 3y+1=3y·31=3·3y. Let us plug these rewrites into our equation:

(3y) 2 4 · 3 · 3y + 27 = 0

(3y) 2 12 ( 3y ) + 27 = 0

This is now a quadratic equation in terms of 3y. Let u=3y. Substituting u gives:

u2 12u + 27 = 0

We can solve for u by factoring this quadratic equation. We are looking for two numbers that multiply to 27 and add to -12. These numbers are -9 and -3.

(u9) (u3) = 0

Thus, we have two possible values for u: u=9 and u=3. We must analyze both cases to find all possible values of x.

Case 1: u=9
Since u=3y, we have 3y=9. Because 9=32, it follows that y=2.

Recall that y=x2+2x3. Substituting y=2 yields:

x2 + 2x 3 = 2

x2 + 2x 5 = 0

Let the roots of this quadratic equation be x1 and x2. According to Vieta's formulas, for any quadratic equation ax2+bx+c=0, the product of the roots is ca. Therefore, the product of roots for this equation is x1·x2=51=5.

Case 2: u=3
Since u=3y, we have 3y=3. Because 3=31, it follows that y=1.

Again, using y=x2+2x3 and substituting y=1 yields:

x2 + 2x 3 = 1

x2 + 2x 4 = 0

Let the roots of this quadratic equation be x3 and x4. Using Vieta's formulas, the product of roots for this equation is x3·x4=41=4.

The problem asks for the product of all possible values of x. This means we must multiply the products of the roots from both cases together:

Total Product = (x1·x2) · (x3·x4)

Total Product = (5) · (4) = 20

Therefore, the product of all possible values of x is 20.

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