Triangle Side Analysis: Is 19+X = 7X+1 = 25-X an Equilateral Triangle?

Equilateral Triangles with Algebraic Expressions

Given the size of the 3 sides of the triangle, is it an equilateral triangle?

19+X19+X19+XAAABBBCCC7X+125-X

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:10 Let's check if the triangle is equilateral.
00:13 Assume the triangle is equilateral. First, we'll find the value of X. Then, we'll verify it.
00:19 Set the two sides equal to find X.
00:23 Now, solve for X. Isolate X on one side of the equation.
00:37 This is X when the sides are equal. Let's verify this assumption.
00:42 Substitute X back into each side. Check if all the sides are equal.
00:48 Here's the value of one side with X substituted in.
00:52 Now, substitute X into the second side.
00:56 Do the same for the third side. Yes, the triangle is equilateral!
01:01 And that's how we solve the problem. Great job!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Given the size of the 3 sides of the triangle, is it an equilateral triangle?

19+X19+X19+XAAABBBCCC7X+125-X

2

Step-by-step solution

To solve this problem, we will follow these steps:

  • Step 1: Calculate when 19+X=7X+1 19 + X = 7X + 1 .
  • Step 2: Calculate when 7X+1=25X 7X + 1 = 25 - X .
  • Step 3: Calculate when 25X=19+X 25 - X = 19 + X .
  • Step 4: Check that these conditions are satisfied simultaneously for the triangle to be equilateral.

Step 1: Solve 19+X=7X+1 19 + X = 7X + 1 .

Rearranging terms, we get 191=7XX 19 - 1 = 7X - X .

This simplifies to 18=6X 18 = 6X , giving X=3 X = 3 .

Step 2: Solve 7X+1=25X 7X + 1 = 25 - X .

Rearranging terms, we get 7X+X=251 7X + X = 25 - 1 .

This simplifies to 8X=24 8X = 24 , giving X=3 X = 3 .

Step 3: Solve 25X=19+X 25 - X = 19 + X .

Rearranging terms, we get 2519=X+X 25 - 19 = X + X .

This simplifies to 6=2X 6 = 2X , giving X=3 X = 3 .

We find that all conditions are satisfied when X=3 X = 3 , and thus all sides are equal at this value.

The side lengths with X=3 X = 3 are:

  • 19+3=22 19 + 3 = 22
  • 7(3)+1=22 7(3) + 1 = 22
  • 253=22 25 - 3 = 22

All sides become equal with X=3 X = 3 , thus the triangle is equilateral.

The solution to the problem is Yes.

3

Final Answer

Yes

Key Points to Remember

Essential concepts to master this topic
  • Definition: All three sides must be equal for equilateral triangle
  • Method: Set each pair equal: 19+X=7X+1 gives X=3
  • Verify: Substitute X=3: all sides equal 22 units ✓

Common Mistakes

Avoid these frequent errors
  • Only checking if two sides are equal
    Don't just solve 19+X=7X+1 and assume it's equilateral = incomplete solution! You must verify all three pairs of sides are equal simultaneously. Always check that all three equations: 19+X=7X+1, 7X+1=25-X, and 25-X=19+X give the same X value.

Practice Quiz

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Is the triangle in the drawing a right triangle?

FAQ

Everything you need to know about this question

Do I really need to solve all three equations?

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Yes! For an equilateral triangle, all three sides must be equal. You need to verify that all three pairs of equations give the same value of X. If even one pair gives a different answer, it's not equilateral.

What if I get different X values from different equations?

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If you get different X values, then the triangle cannot be equilateral for any value of X. This means the answer would be 'No' - the triangle is not equilateral.

How do I solve equations like 19+X=7X+1?

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Move all X terms to one side and constants to the other:

  • Start: 19+X=7X+1 19 + X = 7X + 1
  • Subtract X: 19=6X+1 19 = 6X + 1
  • Subtract 1: 18=6X 18 = 6X
  • Divide by 6: X=3 X = 3

Why do all my equations give X=3?

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Great! When all equations give the same X value, it means there exists a value that makes all sides equal. This confirms the triangle can be equilateral when X=3.

Should I calculate the actual side lengths?

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Yes! It's good practice to substitute X=3 back: 19+3=22, 7(3)+1=22, and 25-3=22. Since all sides equal 22, you can confidently say it's equilateral.

What if the side lengths came out negative?

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Negative side lengths are impossible in geometry! If substituting your X value gives negative lengths, then no valid triangle exists for that value, even if the algebra works out.

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