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• We know that,
x³/3 = 3x²/3
= x²
• Similarly,
5x²/2 = 2*5x/2
= 5x
• 6x is a constant. So, its differentiation becomes 0.
Step - I :-
Now,
y = x³/3 + 5x²/2 + 6x
⇒dy/dx = y' = x² + 5x + 0 = 0
⇒y' = x² + 5x = 0
⇒y' = x(x + 5) = 0
⇒ x = 0, or x = -5
Step - II :-
y" = dy'/dx = x² + 5x
⇒y" = 2x + 5
⇒y" = 2(0) + 5 or y" = 2(-5) + 5
⇒y" = 0 + 5 or y" = -10 + 5
⇒y" = 5 or y" = -5
5 > 0 and -5 < 0
So, 5 is minima and -5 is maxima.
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