If has extrema at and

MATHEMATICS · Single correct · A Level · Mathematics · Differentiation · Differentiation

Problem

If y=alog⁡x+bx2+xy=a\log x+bx^2+x has extrema at x=1x=1 and x=2x=2, then (a,b)=(a,b)= (a) (1,12)\left(1,\frac{1}{2}\right) (b) (12,2)\left(\frac{1}{2},2\right) (c) (2,−12)\left(2,-\frac{1}{2}\right) (d) (−23,−16)\left(-\frac{2}{3},-\frac{1}{6}\right)

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