Solve the Triangle Symbol Equation: △ - 9 = 20

Linear Equations with Symbol Variables

Determine the numerical value of the triangle:

If

9=20 \triangle-9=20

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Determine the numerical value of the triangle:

If

9=20 \triangle-9=20

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Start with the equation: 9=20 \triangle - 9 = 20
  • Add 9 to both sides to isolate \triangle .

Now, let's carry out these steps:

Starting with the equation 9=20 \triangle - 9 = 20 .
To find \triangle , we add 9 to both sides:
9+9=20+9 \triangle - 9 + 9 = 20 + 9

Simplifying this gives us:
=29 \triangle = 29

Therefore, the numerical value represented by \triangle is 29 \boxed{29} .

Looking at the multiple-choice options, we find that 29 29 matches choice 3.

3

Final Answer

29 29

Key Points to Remember

Essential concepts to master this topic
  • Variable Isolation: Add or subtract to move numbers away from variable
  • Addition Property: Add 9 to both sides: 9+9=20+9 \triangle - 9 + 9 = 20 + 9
  • Check: Substitute 29 back into original equation: 29 - 9 = 20 ✓

Common Mistakes

Avoid these frequent errors
  • Adding 9 to only one side of the equation
    Don't add 9 to just the left side = unbalanced equation with wrong answer! This violates the fundamental rule that whatever you do to one side, you must do to the other. Always add or subtract the same number from both sides to maintain equality.

Practice Quiz

Test your knowledge with interactive questions

If we have 67 blocks in total, how many blocks will remain if we remove 5 tens and 4 ones?

FAQ

Everything you need to know about this question

Why can't I just move the 9 to the other side without adding?

+

When you "move" a number across the equals sign, you're actually adding or subtracting it from both sides! The shortcut is that -9 becomes +9 when moved, but the full step is adding 9 to both sides.

What does the triangle symbol represent?

+

The triangle \triangle is just a variable like x or y! It represents an unknown number that we need to find. You can use any symbol as a variable in algebra.

How do I know which operation to use?

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Look at what's happening to your variable! If 9 is being subtracted from \triangle , then add 9 to both sides to undo it. Always do the opposite operation.

What if I get a different answer when I check?

+

If substituting your answer doesn't work, you made an error! Go back and check your arithmetic carefully. Make sure you added the same number to both sides of the equation.

Can this method work for any one-step equation?

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Absolutely! Whether it's addition, subtraction, multiplication, or division, always do the opposite operation to both sides to isolate your variable.

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