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The function f(x)=x2−4x+6f(x) = x^2 - 4x + 6 is

(A) Strictly decreasing on (−∞,2)∪(2,∞)(-\infty, 2) \cup (2, \infty)

(B) Strictly increasing on (2,∞)(2, \infty)

(C) Strictly increasing on (−∞,∞)(-\infty, \infty)

(D) Strictly decreasing on (−∞,2)(-\infty, 2)

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

The function f(x)=x2−4x+6f(x) = x^2 - 4x + 6 needs to be analyzed for intervals where it is strictly increasing or decreasing.

To determine where the function is increasing or decreasing, find the derivative:

f′(x)=2x−4f'(x) = 2x - 4


Setting the derivative equal to zero to find the critical point:

2x−4=02x - 4 = 0

2x=42x = 4

x=2x = 2


For x<2x < 2, test a value such as x=0x = 0:

f′(0)=2(0)−4=−4f'(0) = 2(0) - 4 = -4

Since f′(0)<0f'(0) < 0, the function is strictly decreasing on (−∞,2)(-\infty, 2).


For x>2x > 2, test a value such as x=3x = 3:

f′(3)=2(3)−4=2f'(3) = 2(3) - 4 = 2

Since f′(3)>0f'(3) > 0, the function is strictly increasing on (2,∞)(2, \infty).


Evaluating the given options:

(A) Strictly decreasing on (−∞,2)∪(2,∞)(-\infty, 2) \cup (2, \infty) is false, as the function is increasing on (2,∞)(2, \infty).

(B) Strictly increasing on (2,∞)(2, \infty) is true.

(C) Strictly increasing on (−∞,∞)(-\infty, \infty) is false, as the function is decreasing on (−∞,2)(-\infty, 2).

(D) Strictly decreasing on (−∞,2)(-\infty, 2) is true.

Therefore, options (B) and (D) are correct.

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