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If the polynomial \(ax^2 + bx + 5\) leaves a remainder \(3\) when divided by \(x - 1\), and a remainder \(2\) when divided by \(x + 1\), then \(2b - 4a\) equals

Question and options

If the polynomial ax2+bx+5ax^2 + bx + 5 leaves a remainder 33 when divided by x−1x - 1, and a remainder 22 when divided by x+1x + 1, then 2b−4a2b - 4a equals
  1. 10
  2. 9
  3. 12
  4. 11

Answer and explanation

Correct answer: D - 11

The value of 2b−4a2b-4a is 1111. Evaluating the polynomial at 11 and −1-1 gives a+b=−2a+b=-2 and a−b=−3a-b=-3, so a=−52a=-\frac52 and b=12b=\frac12. Reversing the subtraction that finds bb changes 2b2b to −1-1 and gives 99.

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