Math Problem Statement

dont use quadratic formula

The equation (3k - 4)x - 2k^2 x^2 - 2 = 0 has no real roots. Find the possible range of values of k.

Solution

We are given the equation:

(3k4)x2k2x22=0(3k - 4)x - 2k^2 x^2 - 2 = 0

This is a quadratic equation in xx. To find the range of values of kk such that the equation has no real roots, we don't need to use the quadratic formula explicitly, but we can analyze the discriminant.

For a quadratic equation in the form ax2+bx+c=0ax^2 + bx + c = 0, the discriminant is:

Δ=b24ac\Delta = b^2 - 4ac

The quadratic equation has no real roots if Δ<0\Delta < 0.

Step 1: Identify aa, bb, and cc

We rewrite the given equation in standard form:

2k2x2+(3k4)x2=0-2k^2 x^2 + (3k - 4)x - 2 = 0

Here, a=2k2a = -2k^2, b=3k4b = 3k - 4, and c=2c = -2.

Step 2: Compute the discriminant

The discriminant is given by:

Δ=b24ac=(3k4)24(2k2)(2)\Delta = b^2 - 4ac = (3k - 4)^2 - 4(-2k^2)(-2)

First, simplify each term:

  • (3k4)2=9k224k+16(3k - 4)^2 = 9k^2 - 24k + 16
  • 4(2k2)(2)=16k24(-2k^2)(-2) = 16k^2

Thus, the discriminant becomes:

Δ=(9k224k+16)16k2=9k216k224k+16\Delta = (9k^2 - 24k + 16) - 16k^2 = 9k^2 - 16k^2 - 24k + 16

Simplifying:

Δ=7k224k+16\Delta = -7k^2 - 24k + 16

Step 3: Set Δ<0\Delta < 0

To ensure no real roots, we set the discriminant less than 0:

7k224k+16<0-7k^2 - 24k + 16 < 0

Now, we solve this inequality for kk.

Step 4: Solve the quadratic inequality

First, multiply the inequality by 1-1 (which reverses the inequality sign):

7k2+24k16>07k^2 + 24k - 16 > 0

Next, solve the corresponding quadratic equation:

7k2+24k16=07k^2 + 24k - 16 = 0

Using the discriminant method (this is for the kk-values of the boundary points):

Δk=2424(7)(16)=576+448=1024\Delta_k = 24^2 - 4(7)(-16) = 576 + 448 = 1024

So, the solutions for kk are:

k=24±10242×7=24±3214k = \frac{-24 \pm \sqrt{1024}}{2 \times 7} = \frac{-24 \pm 32}{14}

This gives:

k1=24+3214=814=47,k2=243214=5614=4k_1 = \frac{-24 + 32}{14} = \frac{8}{14} = \frac{4}{7}, \quad k_2 = \frac{-24 - 32}{14} = \frac{-56}{14} = -4

Thus, the quadratic inequality has roots at k=47k = \frac{4}{7} and k=4k = -4.

Step 5: Determine the intervals

Since the parabola opens upwards (because the coefficient of k2k^2 is positive), the solution to 7k2+24k16>07k^2 + 24k - 16 > 0 lies outside the interval between the roots. Therefore, the inequality is satisfied for:

k<4ork>47k < -4 \quad \text{or} \quad k > \frac{4}{7}

Final Answer:

The range of values of kk for which the equation has no real roots is:

k<4ork>47k < -4 \quad \text{or} \quad k > \frac{4}{7}


Would you like a more detailed explanation of any step or further assistance? Here are some related questions to explore:

  1. How can we solve quadratic inequalities algebraically?
  2. What are the different conditions for quadratic equations having real, complex, or no solutions?
  3. How do we determine the nature of roots without using the quadratic formula?
  4. Can the discriminant method be applied to higher-degree polynomials?
  5. How does multiplying an inequality by a negative number affect the inequality sign?

Tip: Always remember to reverse the inequality sign when multiplying both sides by a negative number in an inequality.

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Math Problem Analysis

Mathematical Concepts

Quadratic Inequalities
Discriminant Analysis

Formulas

Discriminant: Δ = b^2 - 4ac
Quadratic formula: ax^2 + bx + c = 0

Theorems

Discriminant Theorem: A quadratic equation has no real roots if Δ < 0
Quadratic Inequality Theorem

Suitable Grade Level

Grades 10-12