Find local maximum and local minimum values of the function f given by
f (a) = 3x4 + 4x3 – 12x2 + 12
f (x) = 3 x4 + 4 x3 – 12 x2 + 12
f ' (x) = 12 x3 + 12 x2 – 24 x = 12 x (x2 + x – 2)
f ' (x) = 12 x (x – 1) (x + 2)
f ' (x) = 0 ⇒ 12 a (x – 1) (x + 2) = 0
∴ x = 0, 1, – 2
f ' (x) = 36 x2 + 24 x – 24
At x = 0, f ' (x) = 0 + 0 24 = – 24 < 0
∴ x = 0 is a point of local maximum
and local maximum value = 0 + 0 – 0 + 12 = 12
At x = 1, f ' (x) = 36 + 24 – 24 = 36 > 0
∴ x = 1 is a point of local minima
and local minimum value = 3+ 4 – 12 + 12 = 7
At x = – 2, f ' (x) = 36 (4) + 24 (– 2) – 24 = 72 > 0
∴ x = – 2 is a point of local minima
and local minimum value = 3 (–2)4 + 4 (–2)3 – 12(–2)2 + 12
= 3 (16) + 4 (– 8) – 12 (4) + 12 = 48– 32 – 48 + 12 = – 20