Basic Mathematics & Logarithm
Algebraic identities
Grade 11

Question:

<p>Value of \(\dfrac{(x-1)^3 + (2x-1)^3 - (3x-2)^3}{(x-1)(2x-1)(3x-2)}\) is equal to:</p>
<p>\(-3\)</p>
<p>0</p>
<p>1</p>
<p>3</p>

Step-by-Step Solution

Key Concept: Recognize that the numerator has the form a³ + b³ + c³ where a + b + c = 0, which triggers the identity a³ + b³ + c³ = 3abc when a + b + c = 0.
**Step 1:** Define the terms for the algebraic identity. Let $A = x-1$, $B = 2x-1$, and $C = -(3x-2)$. **Step 2:** Verify the condition for the algebraic identity. Calculate the sum $A+B+C$: $$A+B+C = (x-1) + (2x-1) + (-(3x-2))$$ $$A+B+C = x-1 + 2x-1 - 3x+2$$ $$A+B+C = (x+2x-3x) + (-1-1+2)$$ $$A+B+C = 0 + 0$$ $$A+B+C = 0$$ Since $A+B+C=0$, the algebraic identity $A^3+B^3+C^3 = 3ABC$ applies. **Step 3:** Apply the identity to the numerator of the given expression. The numerator of the given expression is $(x-1)^3 + (2x-1)^3 - (3x-2)^3$. This can be rewritten as $(x-1)^3 + (2x-1)^3 + (-(3x-2))^3$. Using the identity with $A=(x-1)$, $B=(2x-1)$, and $C=-(3x-2)$: $$(x-1)^3 + (2x-1)^3 + (-(3x-2))^3 = 3(x-1)(2x-1)(-(3x-2))$$ **Step 4:** Substitute the simplified numerator back into the original expression and simplify. The given expression is: $$\dfrac{(x-1)^3 + (2x-1)^3 - (3x-2)^3}{(x-1)(2x-1)(3x-2)}$$ Substitute the result from Step 3 into the numerator: $$ = \dfrac{3(x-1)(2x-1)(-(3x-2))}{(x-1)(2x-1)(3x-2)}$$ Assuming $(x-1)(2x-1)(3x-2) \neq 0$, the common terms $(x-1)$, $(2x-1)$, and $(3x-2)$ cancel out: $$ = 3 \cdot (-1)$$ $$ = -3$$
Correct Answer: A

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