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JEE MainMathematicsModerateMonotonocity

If the function f(x)=t+3x−x2x−4f(x) = \frac{t + 3x - x^{2}}{x - 4} where
is a parameter has a local minima and a local maxima, then the

range of values of is.

Show answer and solution
f(x)=t+3x−x2x−4;f′(x)=(x−4)(3−2x)−(t+3x−x2)(x−4)2f(x) = \frac{t + 3x - x^{2}}{x - 4};f^{'}(x) = \frac{(x - 4)(3 - 2x) - \left( t + 3x - x^{2} \right)}{(x - 4)^{2}}
for maximum or minimum, f ' (x) = 0

- 2x^2 + 11x - 12 - t - 3x + x^2 = 0

- x^2 + 8x - (12 + t) = 0

for one M and m

D > 0

64 - 4(12 + t) > 0

16 - 12 - t > 0

⇒\Rightarrow 4 > t or t < 4]

Source: Grass-G / M-12 Mathematics Paper 2 Nov.docx

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