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Zorluk: OrtaLinear Inequalities and Absolute Value

If xx is an integer that satisfies both ∣2x−3∣≤9|2x - 3| \le 9 and 5−3x−2>4\frac{5 - 3x}{-2} > 4, how many possible values of xx exist?

  1. 2Cevap
  2. B
    3
  3. C
    5
  4. D
    8
  5. E
    10

Cevap

There are 2 possible integer values of xx (specifically x=5x = 5 and x=6x = 6).
Solving ∣2x−3∣≤9|2x - 3| \le 9 yields −3≤x≤6-3 \le x \le 6. Solving 5−3x−2>4\frac{5 - 3x}{-2} > 4 requires reversing the inequality sign twice (first when multiplying by −2-2, giving 5−3x<−85 - 3x < -8, and second when dividing by −3-3, giving x>133≈4.33x > \frac{13}{3} \approx 4.33). The integers satisfying both −3≤x≤6-3 \le x \le 6 and x>4.33x > 4.33 are 55 and 66, which gives exactly 2 possible values.

Adım Adım Çözüm

1
Solve the absolute value inequality ∣2x−3∣≤9|2x - 3| \le 9.
−9≤2x−3≤9  ⟹  −6≤2x≤12  ⟹  −3≤x≤6-9 \le 2x - 3 \le 9 \implies -6 \le 2x \le 12 \implies -3 \le x \le 6.
An absolute value inequality of the form ∣u∣≤k|u| \le k unfolds into the compound inequality −k≤u≤k-k \le u \le k.
2
Solve the linear inequality 5−3x−2>4\frac{5 - 3x}{-2} > 4.
5−3x<−8  ⟹  −3x<−13  ⟹  x>133≈4.335 - 3x < -8 \implies -3x < -13 \implies x > \frac{13}{3} \approx 4.33.
Multiplying or dividing an inequality by a negative number requires reversing the direction of the inequality sign at each step.
3
Find the intersection of the two solution sets for integer values of xx.
The range of valid values is 4.33<x≤64.33 < x \le 6. The integers in this interval are x=5x = 5 and x=6x = 6.
Combining −3≤x≤6-3 \le x \le 6 and x>4.33x > 4.33 restricts xx to integer values strictly greater than 4.334.33 and less than or equal to 66.
4
Count the valid integer values.
There are 2 integers (55 and 66).
Direct counting of the valid integer set {5,6}\{5, 6\}.

Anahtar Kavram

Solving absolute value inequalities and compound linear inequalities with negative multipliers
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