If $x = -3$, then $x^3 - x^2 - x$ will be equal to
Aptitude
Simplification
Difficulty: Easy
Choose an option
-
A-33
-
B-27
-
C15
-
D54
Answer
Correct Answer: -33
Explanation
### Concept & Formula
This is a direct polynomial evaluation problem. The goal is to substitute a specific value into an algebraic expression and calculate the result.
The core concept tested is the rule of signs for exponents:
* A negative base raised to an **odd** power results in a **negative** number.
* A negative base raised to an **even** power results in a **positive** number.
### Step-by-Step Solution
Given the expression:
$$x^3 - x^2 - x$$
* **Step 1: Substitute the value**
Replace every instance of $x$ with $(-3)$. Use parentheses to avoid sign errors:
$$(-3)^3 - (-3)^2 - (-3)$$
* **Step 2: Evaluate the Exponents**
Calculate the cube: $(-3)^3 = -3 \times -3 \times -3 = -27$
Calculate the square: $(-3)^2 = -3 \times -3 = 9$
* **Step 3: Rewrite the expression**
Substitute the expanded values back into the equation:
$$-27 - (9) - (-3)$$
* **Step 4: Resolve the signs and compute**
Subtracting a negative is the same as addition:
$$-27 - 9 + 3$$
$$-36 + 3 = -33$$
### Exam Strategy & Shortcut
When substituting negative values, immediately write down the expected sign for each term before doing the multiplication.
Term 1 ($x^3$): Negative
Term 2 ($-x^2$): Negative (because $x^2$ is positive, but it's subtracted)
Term 3 ($-x$): Positive (double negative)
This mental check confirms the structure is $- A - B + C$, heavily minimizing careless sign-flipping mistakes under pressure.
### Common Pitfall
A very common mistake is improperly evaluating $-x^2$. Students often write $-(-3)^2 = +9$, erroneously multiplying the outer negative by the inner negative before squaring. Exponents must always be resolved before the subtraction operator is applied outside.
### Final Answer
**Therefore, the correct answer is -33.**