Math Problem Statement

Point K is between points J and L if JK=x2x^2-4x KL = 3x-2 and JL = 28 find JK and KL

Solution

To solve for the lengths of JKJK and KLKL, we need to use the fact that point KK lies between points JJ and LL. This implies that:

JK+KL=JLJK + KL = JL

Given:

  • JK=x24xJK = x^2 - 4x
  • KL=3x2KL = 3x - 2
  • JL=28JL = 28

We can set up the equation:

(x24x)+(3x2)=28(x^2 - 4x) + (3x - 2) = 28

Simplifying:

x24x+3x2=28x^2 - 4x + 3x - 2 = 28

x2x2=28x^2 - x - 2 = 28

Next, subtract 28 from both sides:

x2x30=0x^2 - x - 30 = 0

Now, solve this quadratic equation using the quadratic formula:

x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

For x2x30=0x^2 - x - 30 = 0, a=1a = 1, b=1b = -1, and c=30c = -30. Substituting these values:

x=(1)±(1)24(1)(30)2(1)x = \frac{-(-1) \pm \sqrt{(-1)^2 - 4(1)(-30)}}{2(1)}

x=1±1+1202x = \frac{1 \pm \sqrt{1 + 120}}{2}

x=1±1212x = \frac{1 \pm \sqrt{121}}{2}

x=1±112x = \frac{1 \pm 11}{2}

So, xx can be:

x=122=6orx=102=5x = \frac{12}{2} = 6 \quad \text{or} \quad x = \frac{-10}{2} = -5

Case 1: x=6x = 6

Substitute x=6x = 6 into the expressions for JKJK and KLKL:

JK=624(6)=3624=12JK = 6^2 - 4(6) = 36 - 24 = 12

KL=3(6)2=182=16KL = 3(6) - 2 = 18 - 2 = 16

Check if JK+KL=JLJK + KL = JL:

12+16=2812 + 16 = 28

This is correct.

Case 2: x=5x = -5

Substitute x=5x = -5:

JK=(5)24(5)=25+20=45JK = (-5)^2 - 4(-5) = 25 + 20 = 45

KL=3(5)2=152=17KL = 3(-5) - 2 = -15 - 2 = -17

However, a negative length for KLKL is not physically meaningful, so x=5x = -5 is not a valid solution.

Conclusion

The valid solution is x=6x = 6, so:

JK=12,KL=16JK = 12, \quad KL = 16

Do you want details or have any questions?

Here are 5 related questions:

  1. How would the equation change if point K was outside the segment JL?
  2. What happens if we had a cubic equation instead of a quadratic one?
  3. How can we geometrically represent this situation?
  4. What is the significance of discarding the negative root in this problem?
  5. How do you solve quadratic equations by factoring?

Tip: Always check the physical meaning of your solutions, especially when dealing with geometric problems.

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Math Problem Analysis

Mathematical Concepts

Geometry
Quadratic Equations

Formulas

Quadratic formula

Theorems

Segment Addition Postulate

Suitable Grade Level

High School