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The expression ax2 + bx + c equals 5 at x = 1. If its...

Mathematics
JAMB 2000

The expression ax2 + bx + c equals 5 at x = 1. If its derivative is 2x + 1, what are the values of a, b, c respectively?
  • A. 1, 3, 1
  • B. 1, 2, 1
  • C. 2, 1, 1
  • D. 1, 1, 3
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Correct Answer: Option D
Explanation
At x = 1, substituting x = 1 in the equation: ax2 + bx + c = 5;
f(1) => a + b + c = 5 .....(1)

Taking the first derivative of f(x) in the original equation gives dy/dx = 2ax + b = 2x + 1 (given)....(2)

From (2),=> b = 1, and 2ax = 2x, => a = 1.

substituting into (1) 1 + 1 + c = 5, => c = 5 - 2 = 3

Thus a = 1, b = 1 and c = 3

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WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC offline past questions - with all answers and explanations in one app - Download for free
WAEC Past Questions, Objective & Theory, Study 100% offline, Download app now - 24709
Post-UTME Past Questions - Original materials are available here - Download PDF for your school of choice + 1 year SMS alerts
WAEC May/June 2024 - Practice for Objective & Theory - From 1988 till date, download app now - 99995