WAEC 2013 Mathematics · Question 25
Given that (x + 2)(x2 - 3x + 2) + 2(x + 2)(x - 1) = (x + 2) M, find M
Options
- A.(x + 2)2
- B.x(x + 2)
- C.xv + 2
- D.x2 - x
Answer: D. x2 - x
Explanation written with AI and checked against the answer key
Analyze the question: Both terms on the left have a common factor (x + 2). We factor it out and see what is left, which is M.
Concept: Common factor extraction: a·b + a·c = a(b + c).
Solution:
(x + 2)(x² − 3x + 2) + 2(x + 2)(x − 1)
Factor out (x + 2):
= (x + 2)[(x² − 3x + 2) + 2(x − 1)]
Expand inside the bracket:
= (x + 2)[x² − 3x + 2 + 2x − 2]
= (x + 2)[x² − x]
Comparing with (x + 2)M:
M = x² − x
Checking the options:
- A. (x + 2)²: no
- B. x(x + 2) = x² + 2x: no
- C. "xv + 2" looks like a typing error and is not equivalent to x² − x
- D. x² − x: matches
Tip: When you see the same bracket in every term, factor it out immediately. It saves you from expanding long cubic expressions. Also, x² − 3x + 2 = (x − 1)(x − 2), so the bracket could be written as (x − 1)[(x − 2) + 2] = (x − 1)x, which gives the same result.
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