If 4x - 5 = 3x - 1, then what is the numerical value of (x + 4)^2?

Difficulty: Easy

Correct Answer: 64

Explanation:


Introduction / Context:
This question checks your understanding of solving a simple linear equation in one variable and then using that solution to evaluate a related expression. It is a classic aptitude style problem where you first determine the value of x and then substitute this value into (x + 4)^2 to get a numerical result.


Given Data / Assumptions:

  • The equation 4x - 5 = 3x - 1 is given.
  • We need to find the numerical value of (x + 4)^2.
  • x is a real number and normal arithmetic rules apply.


Concept / Approach:
The approach is to first isolate x by collecting all x terms on one side of the equation and constants on the other. Once x is known, you substitute it into (x + 4)^2 and simplify using basic algebra. Squaring a binomial means multiplying the same bracket by itself and computing the result.


Step-by-Step Solution:

Step 1: Start from the equation 4x - 5 = 3x - 1. Step 2: Subtract 3x from both sides: 4x - 3x - 5 = -1, which simplifies to x - 5 = -1. Step 3: Add 5 to both sides: x = -1 + 5 = 4. Step 4: Now compute the expression (x + 4)^2 using x = 4. Step 5: x + 4 = 4 + 4 = 8. Step 6: Square this value: (x + 4)^2 = 8^2 = 64.


Verification / Alternative check:
You can verify by substituting x = 4 back into the original equation. Left-hand side: 4*4 - 5 = 16 - 5 = 11. Right-hand side: 3*4 - 1 = 12 - 1 = 11. Since both sides are equal, x = 4 is correct. The computed value of (x + 4)^2 = 64 is therefore reliable.


Why Other Options Are Wrong:

16: corresponds to 4^2, which would be (x)^2, not (x + 4)^2. 32: might come from incorrectly computing 8 * 4 instead of 8^2. 8: is just x + 4, not its square. 36: would appear if someone mistakenly used (x - 2)^2 with x = 8 or another incorrect manipulation.


Common Pitfalls:
Students sometimes forget that (x + 4)^2 means (x + 4) multiplied by itself and not simply doubling x + 4. Another frequent mistake is mismanaging signs when moving terms across the equality sign. Carefully isolating x and then squaring only after substitution avoids these errors.


Final Answer:
64

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