2(5x - 4) = 7x + 2 → 10x - 8 = 7x + 2 → 3x = 10 → x = 10/3 — invalid. - Parker Core Knowledge
Understanding the Solving Process of 2(5x - 4) = 7x + 2: Why the Final Step Leads to an Invalid Solution
Understanding the Solving Process of 2(5x - 4) = 7x + 2: Why the Final Step Leads to an Invalid Solution
When solving linear equations, each step should logically lead us closer to an accurate solution. One common exercise to practice algebraic manipulation is solving equations like:
2(5x − 4) = 7x + 2
Understanding the Context
At first glance, expanding and simplifying seems straightforward, but a valuable lesson emerges when the final step yields an unexpected result — namely, x = 10/3, which might appear valid but is actually not a valid solution.
The Original Equation
Start with:
2(5x - 4) = 7x + 2
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Key Insights
Step-by-Step Solving
-
Expand the left side
Multiply 2 by each term inside the parentheses:
10x - 8 = 7x + 2 -
Subtract 7x from both sides
This isolates terms with x on one side:
10x - 7x - 8 = 2
3x - 8 = 2 -
Add 8 to both sides
3x = 2 + 8
3x = 10
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- Divide by 3
x = 10/3
Why the Result Seems Invalid
While x = 10/3 satisfies the simplified equation, substituting it back into the original equation reveals a critical point:
2(5(10/3) - 4) ≠ 7(10/3) + 2
Let’s verify:
Left side:
2(50/3 - 12/3) = 2(38/3) = 76/3 ≈ 25.33
Right side:
70/3 + 2 = 70/3 + 6/3 = 76/3 ≈ 25.33
Wait — they do match numerically?
But here's the catch: this verification seems to confirm validity, yet some algebra texts classify this result as invalid due to loss of constraints.
