Math Problem Statement

if k is a positive integer, find the maximum value of k such that (k+8)x² + (k-2)x-3=0 has real roots

Solution

To find the maximum value of kk such that the quadratic equation

(k+8)x2+(k2)x3=0(k+8)x^2 + (k-2)x - 3 = 0

has real roots, we need to ensure that the discriminant of the equation is non-negative.

Step 1: Identify the Discriminant Condition for Real Roots

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

Δ=b24ac\Delta = b^2 - 4ac

The roots are real if and only if Δ0\Delta \geq 0.

Step 2: Define aa, bb, and cc

In our equation:

  • a=k+8a = k + 8
  • b=k2b = k - 2
  • c=3c = -3

Step 3: Compute the Discriminant

Substitute these values into the discriminant formula:

Δ=(k2)24(k+8)(3)\Delta = (k - 2)^2 - 4(k + 8)(-3)

Expanding this:

Δ=(k2)2+12(k+8)\Delta = (k - 2)^2 + 12(k + 8)

Calculate each term:

  1. (k2)2=k24k+4(k - 2)^2 = k^2 - 4k + 4
  2. 12(k+8)=12k+9612(k + 8) = 12k + 96

So,

Δ=k24k+4+12k+96\Delta = k^2 - 4k + 4 + 12k + 96

Combine like terms:

Δ=k2+8k+100\Delta = k^2 + 8k + 100

Step 4: Ensure the Discriminant is Non-negative

For the quadratic equation to have real roots, we need:

k2+8k+1000k^2 + 8k + 100 \geq 0

Step 5: Analyze the Quadratic Expression

The expression k2+8k+100k^2 + 8k + 100 is always positive for all values of kk since its discriminant (82411008^2 - 4 \cdot 1 \cdot 100) is negative, indicating it has no real roots and opens upwards.

Therefore, no upper limit on kk is needed for real roots to exist. The value of kk can be any positive integer.

Conclusion

The maximum value of kk such that (k+8)x2+(k2)x3=0(k+8)x^2 + (k-2)x - 3 = 0 has real roots is unbounded, meaning kk can be any positive integer.


Would you like further clarification on any part of the solution?

Related Questions:

  1. What if kk were negative? How would the result change?
  2. How would we find the roots if kk were a specific value, like 1 or 2?
  3. Could there be any conditions on kk for complex roots to occur?
  4. What if we were asked for integer solutions for xx given this quadratic?
  5. How would this change if we maximized kk for complex roots instead?

Tip: For any quadratic equation, always check the discriminant to determine the nature of its roots.

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Discriminant

Formulas

Discriminant formula for quadratic equations: Δ = b² - 4ac

Theorems

Real Roots Theorem (discriminant condition)

Suitable Grade Level

Grades 10-12