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JEE MainMathematicsModerateApplication of derivatives

Consider the function
f(x)=x+1x,x∈(12,92)f(x) = x + \frac{1}{x},x \in (\frac{1}{2},\frac{9}{2}). If α\alpha is
the length of interval of decrease and
β\beta be the length of interval
of increase, then
βα\frac{\beta}{\alpha} is ____.

Show answer and solution
f(x)=x+1x,x∈(12,92)f(x) = x + \frac{1}{x},x \in (\frac{1}{2},\frac{9}{2}) is
decreasing in
(12,1)(\frac{1}{2},1) and increasing in (1,92)(1,\frac{9}{2})
α=1−12=12,β=92−1=72\alpha = 1 - \frac{1}{2} = \frac{1}{2},\beta = \frac{9}{2} - 1 = \frac{7}{2}
∴βα=7\therefore\frac{\beta}{\alpha} = 7

Source: Grass-G / M-20 Mathematics Paper 12 Dec.docx

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