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a
Both roots in [a, b]
b
Both roots in (-∞,a)
c
Both roots in (b, +∞)
d
One root in (-∞, a) and the other in (b, +∞)
answer is D.
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Detailed Solution
The equation is x2-(a+b)x+ab-1=0∴ discriminant =(a+b)2-4(ab-1)=(b-a)2+4>0∴ both roots are real. Let them be α,β whereα=(a+b)-(b-)2+42, β=(a+b)+(b-a)2+42Clearly, α<(a+b)-(b-a)22=(a+b)-(b-a)2=a(∵b>a)and β>(a+b)+(b-a)22=a+b+b-a2=bHence, one root α is less than a and the other root β is greater than b.