Advanced MathMediumSum of the coefficients of an expanded square
Advanced Math practice question
When (2x + 3)² is expanded and written as ax² + bx + c, what is the value of a + b + c?
Answer: 25
(2x + 3)² = 4x² + 12x + 9, so a + b + c = 4 + 12 + 9 = 25. (Shortcut: a + b + c is the value at x = 1, which is (2 + 3)² = 25.)
Common wrong answers
- If you answered 5
- 5 is 2 + 3, before squaring.
- If you answered 13
- 13 leaves out the middle term 12x: (2x + 3)² is not 4x² + 9.
- If you answered 19
- 19 comes from a middle term of 6x, forgetting to double 2·3.
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