The value of ξ in the mean value theorem of f(b)−f(a)=(b−a)f′(ξ) for f(x)=Ax2+Bx+C in (a,b) is
A
b+a
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B
b−a
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C
(b+a)2
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D
(b−a)2
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Solution
The correct option is C(b+a)2 f(x)=Ax2+Bx+C f′(x)=2Ax+B f′(ξ)=2Aξ+B
By mean value theorem, we have f′(ξ)==f(b)−f(a)b−a 2Aξ+B=(Ab2+Bb+C)−(Aa2+Ba+C)b−a 2Aξ+B=A(b+a)+B ξ=b+a2