Determining Solutions for 3x + 4 < 9 and x + 5 > 3

Compound Inequalities with Variable Isolation

When are the following inequalities satisfied?

3x+4<9 3x+4<9

3<x+5 3 < x+5

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1

Understand the problem

When are the following inequalities satisfied?

3x+4<9 3x+4<9

3<x+5 3 < x+5

2

Step-by-step solution

To solve the given inequalities, we will handle each one individually and then find the valid range of x x where both are satisfied:

  • First Inequality: 3x+4<9 3x + 4 < 9
    Solve for x x by first subtracting 4 from both sides:
    3x+44<943x<5 3x + 4 - 4 < 9 - 4 \Rightarrow 3x < 5 .
    Next, divide both sides by 3 to solve for x x :
    x<53 x < \frac{5}{3} .
  • Second Inequality: 3<x+5 3 < x + 5
    Solve for x x by subtracting 5 from both sides:
    35<x+552<x 3 - 5 < x + 5 - 5 \Rightarrow -2 < x .

Now we combine the solutions from both inequalities:

  • From the first inequality, we have: x<53 x < \frac{5}{3} .
  • From the second inequality, we have: x>2 x > -2 .

Therefore, combining these results, the solution is the intersection of the two ranges:

2<x<53-2 < x < \frac{5}{3}, which can be expressed as 2<x<123 -2 < x < 1\frac{2}{3} .

The final solution is 2<x<123 -2 < x < 1\frac{2}{3} .

3

Final Answer

2<x<123 -2 < x < 1\frac{2}{3}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Solve each inequality separately, then find the intersection
  • Technique: From 3x + 4 < 9, subtract 4: 3x < 5, divide by 3: x < 5/3
  • Check: Test x = 0: 3(0) + 4 = 4 < 9 ✓ and 0 + 5 = 5 > 3 ✓

Common Mistakes

Avoid these frequent errors
  • Finding union instead of intersection
    Don't combine solutions with 'or' to get all values satisfying either inequality = wrong solution set! This includes values that only satisfy one condition. Always find the intersection using 'and' to get values satisfying both inequalities simultaneously.

Practice Quiz

Test your knowledge with interactive questions

Solve the inequality:


\( 5-3x>-10 \)

FAQ

Everything you need to know about this question

What's the difference between intersection and union of inequalities?

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Intersection (AND) means x must satisfy both inequalities at the same time. Union (OR) means x satisfies at least one inequality. For compound inequalities with 'and', always use intersection!

How do I write the final answer correctly?

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Write it as a compound inequality: 2<x<123 -2 < x < 1\frac{2}{3} . This shows that x is between -2 and 123 1\frac{2}{3} , not including the endpoints.

Why do I get no solution sometimes?

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You get no solution when the two conditions contradict each other, like x < 2 AND x > 5. There's no number that can be both less than 2 and greater than 5 at the same time!

Can I solve both inequalities at once?

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No, solve each inequality separately first. Only after getting both individual solutions should you combine them to find where they overlap.

What if one inequality has ≤ and the other has +

The final answer uses whichever symbol applies. If you have x ≤ 3 and x > -1, your compound inequality becomes 1<x3 -1 < x ≤ 3 .

How do I check my compound inequality answer?

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Pick a test value from your solution interval and substitute it into both original inequalities. If both are true, your answer is correct!

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