Find the value of x for which the function f(x) = 2x3 - x2 - 4x + 4 has a maximum value

Assessment: JAMB UTME - Mathematics - 2007 Subject: General Mathematics

Question 1 Report

Find the value of x for which the function f(x) = 2x3 - x2 - 4x + 4 has a maximum value
Answer Details
f(x) = 2x3 - x2 - 4x + 4
f(x) = 6x2 - 2x - 4 at turning point, f1(x) = 0
6x2 - 2x - 4 = 0, 3x2 - x - 2 = 0, 3x2 - 3x + 2x - 2 = 0
(3x + 2)(x - 1) = 0, x = - 2 3  or 1
f11(x) = 12x - 2,
when x =  2 3 , f11(x) = 12(- 2 3 ) - 2 = -10 < 0

→  f(x) is maximum @ x = - 2 3
when x = 1, f11(x) = 12(1)- 2 = 10 > 0
→  f(x) is maximum @ x = 1

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