Let f be a function defined by f(x)=tan−1(x2+kx+9−x). If range of f(x) lies in the interval (0,π2) for all values of xϵR, then find the maximum integral value of k. ___
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Solution
Since range is a subset of (0,π2) hence x2+(k−1)x+9>0∀xϵR ⇒D<0 (k−1)2−36<0 (k−7)(k+5)<0 k(−5,7) ∴kmax=6