Math Problem Statement

Given that −10≤k≤10 and k is an integer. How many possible integers k so that the following inequality holds? |k-1|(k-6)\le -6

Solution

Given the inequality k1(k6)6|k - 1|(k - 6) \leq -6 and the range 10k10-10 \leq k \leq 10, where kk is an integer, we need to determine how many possible integer values of kk satisfy this inequality.

Step 1: Consider the inequality

The inequality is k1(k6)6|k - 1|(k - 6) \leq -6.

Note that the absolute value k1|k - 1| is always non-negative, so the product k1(k6)|k - 1|(k - 6) is non-negative or zero unless k6k - 6 is negative. The left side must be negative or zero to satisfy 6\leq -6. This implies that the only way for k1(k6)6|k - 1|(k - 6) \leq -6 is for the left side to be negative, and since k10|k - 1| \geq 0, we must have k1(k6)<0|k - 1|(k - 6) < 0.

However, for the left side to equal 6-6 exactly, the product would need to match that value, but it cannot since k1(k6)|k - 1|(k - 6) can't be negative by definition unless the absolute value function is multiplied by a negative term.

Step 2: Break down the inequality

Consider the two cases for the absolute value k1|k - 1|:

  1. Case 1: k10k - 1 \geq 0 (i.e., k1k \geq 1) \ Then k1=k1|k - 1| = k - 1. The inequality becomes: (k1)(k6)6(k - 1)(k - 6) \leq -6

  2. Case 2: k1<0k - 1 < 0 (i.e., k<1k < 1) \ Then k1=(k1)|k - 1| = -(k - 1). The inequality becomes: (k1)(k6)6    (k1)(k6)6-(k - 1)(k - 6) \leq -6 \implies (k - 1)(k - 6) \geq 6

Step 3: Analyze the inequality in both cases

Case 1: k1k \geq 1

The inequality is (k1)(k6)6(k - 1)(k - 6) \leq -6.

Expanding it:

k27k+66k^2 - 7k + 6 \leq -6 k27k+120k^2 - 7k + 12 \leq 0

To solve k27k+120k^2 - 7k + 12 \leq 0, we find the roots of the quadratic equation k27k+12=0k^2 - 7k + 12 = 0 using the quadratic formula:

k=(7)±(7)24(1)(12)2(1)=7±49482=7±12k = \frac{-(-7) \pm \sqrt{(-7)^2 - 4(1)(12)}}{2(1)} = \frac{7 \pm \sqrt{49 - 48}}{2} = \frac{7 \pm 1}{2}

So, the roots are k=4k = 4 and k=3k = 3. The inequality k27k+120k^2 - 7k + 12 \leq 0 holds when 3k43 \leq k \leq 4.

Case 2: k<1k < 1

The inequality is (k1)(k6)6(k - 1)(k - 6) \geq 6.

Expanding it:

k27k+66k^2 - 7k + 6 \geq 6 k27k0k^2 - 7k \geq 0

This inequality holds when k0k \leq 0 or k7k \geq 7.

Step 4: Combine results with the given range 10k10-10 \leq k \leq 10

From Case 1:

  • 3k43 \leq k \leq 4 gives k=3,4k = 3, 4.

From Case 2:

  • k0k \leq 0 gives k=10,9,,0k = -10, -9, \ldots, 0.

Thus, the possible values for kk that satisfy the inequality are: k=10,9,8,7,6,5,4,3,2,1,0,3,4k = -10, -9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 3, 4

Final Count

There are 11+2=1311 + 2 = 13 possible integers for kk that satisfy the inequality.

Would you like further details on any step, or do you have any additional questions?


Related Questions:

  1. How do we solve inequalities involving absolute values and quadratic expressions?
  2. How would the solution change if the inequality was k1(k6)6|k-1|(k-6) \geq -6?
  3. What happens if the range of kk was different?
  4. Can you solve similar inequalities without the integer constraint on kk?
  5. How do absolute value inequalities differ when the constant on the right side is positive?

Tip: Always consider splitting the inequality into cases when dealing with absolute values, as it often simplifies the process of solving the inequality.

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Math Problem Analysis

Mathematical Concepts

Inequalities
Absolute Value
Quadratic Equations

Formulas

Quadratic formula

Theorems

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Suitable Grade Level

High School