Skip to main contentSkip to solution

For the function f(x)=32x4−4x3−45x2+49f(x) = \dfrac{3}{2}x^4 - 4x^3 - 45x^2 + 49. Which of the following statements is/are TRUE ?

A. f(x)f(x) is increasing in (−∞,−3)(-\infty, -3)

B. f(x)f(x) is increasing in (−3,0)∪(5,∞)(-3, 0) \cup (5, \infty)

C. f(x)f(x) is decreasing in (−∞,−3)∪(0,5)(-\infty, -3) \cup (0, 5)

D. f(x)f(x) is decreasing in (−∞,−3)∪(5,∞)(-\infty, -3) \cup (5, \infty)

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

f′(x)=6x3−12x2−90x=6x(x−5)(x+3)f'(x)=6x^3-12x^2-90x=6x(x-5)(x+3), with roots −3,0,5-3,0,5. The sign is negative on (−∞,−3)(-\infty,-3), positive on (−3,0)(-3,0), negative on (0,5)(0,5) and positive on (5,∞)(5,\infty). So f increases on (−3,0)∪(5,∞)(-3,0)\cup(5,\infty) and decreases on (−∞,−3)∪(0,5)(-\infty,-3)\cup(0,5), making B and C true.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question