Application of DerivativeHard
Question
If y = a log x + bx2 + x has its extremum values at x = -1 and x = 2, than
Options
A.a = 2,b = - 1
B.a = 2, b = - 
C.a = - 2, b =
D.None of these
Solution
y = a log x + bx2 + x has extremum at x = - 1 and x = 2
∴
= 0, x = - 1 and x = 2
⇒
+ 2bx + 1 = 0, at x = - 1and x = 2
∴ - a - 2b + 1 = 0 and
+ 4b + 1 = 0
⇒ a = 2 and b = -
∴
= 0, x = - 1 and x = 2⇒
+ 2bx + 1 = 0, at x = - 1and x = 2∴ - a - 2b + 1 = 0 and
+ 4b + 1 = 0 ⇒ a = 2 and b = -
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