Solve for the Unknown: ?-2-(-4)=-20 Step by Step

Linear Equations with Double Negatives

Solve the following expression:

?2(4)=20 \text{?}-2-(-4)=-20

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's find the unknown. Ready, set, go!
00:11 Remember, a negative times a negative, always makes a positive.
00:17 Next, we'll open the parentheses to simplify your expression.
00:22 Now, calculate the operation. You're doing great, keep it up!
00:33 Let's focus on isolating the unknown. Step by step, together!
00:38 Calculate each operation separately. Almost there!
00:47 And that's how we solve this question. Great job!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following expression:

?2(4)=20 \text{?}-2-(-4)=-20

2

Step-by-step solution

Note the following law:

(x)=+ -(-x)=+

Now let's write the exercise in the appropriate form:

?2+4=20 ?-2+4=-20

?2=20 ?-2=-20

We'll move minus 2 to the right side and maintain the appropriate sign:

?=202 ?=-20-2

Now we get:

?=22 ?=-22

3

Final Answer

22 -22

Key Points to Remember

Essential concepts to master this topic
  • Rule: Double negative -(-4) becomes positive: -(-4) = +4
  • Technique: Simplify ? - 2 + 4 = -20 to ? + 2 = -20
  • Check: Substitute -22: (-22) - 2 - (-4) = -22 + 2 = -20 ✓

Common Mistakes

Avoid these frequent errors
  • Keeping the double negative as negative
    Don't treat -(-4) as -4 = wrong simplification to ? - 6 = -20! This ignores the fundamental rule that subtracting a negative equals adding a positive. Always remember -(-x) = +x and convert double negatives first.

Practice Quiz

Test your knowledge with interactive questions

a is negative number.

b is negative number.

What is the sum of a+b?

FAQ

Everything you need to know about this question

Why does -(-4) become +4?

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Think of it as "the opposite of the opposite". If -4 is negative, then the opposite of -4 is positive 4. It's like saying "not not happy" means happy!

Should I solve from left to right?

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Always handle double negatives first! Don't work left to right with operations until you've simplified (4) -(-4) to +4 +4 . Order of operations comes after simplifying signs.

How do I move terms to the other side correctly?

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When moving a term across the equals sign, change its sign. So ?+2=20 ? + 2 = -20 becomes ?=202 ? = -20 - 2 because +2 becomes -2.

What if I get confused with all the negative signs?

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Take it step by step! First handle double negatives, then combine like terms on each side, finally isolate the unknown. Write each step clearly to avoid sign errors.

Is there a pattern for double negatives?

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  • -(-positive) = +positive
  • -(-negative) = +negative

The key is: subtracting always changes the sign of what you're subtracting!

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