Answer:
The correct option is:
The function is decreasing for all real values of x where x < 1.5.
Step-by-step explanation:
We are given a function f(x) which is a product of two linear polynomial as:
[tex]f(x)=(x-4)(x+1)[/tex]
Now, we know that on multiplying the two linear polynomial we will obtain a quadratic polynomial.
So, the function f(x) will be represented as:
[tex]f(x)=x(x+1)-4(x+1)\\\\f(x)=x^2+x-4x-4\\\\f(x)=x^2-3x-4[/tex]
So, we will plot the graph of the function and check which statements about the function hold true.
1)
The function is increasing for all real values of x where x < 0.
This statement is false.
Since we get from the graph that function f(x) is decreasing for x<0.
2)
The function is increasing for all real values of x where x < –1 and where x > 4.
This option is incorrect as the function is decreasing for x<-1
whereas it is increasing for x>4.
3)
The function is decreasing for all real values of x where –1 < x < 4.
This option is incorrect.
Since, the function is both decreasing as well as increasing in the interval (-1,4).
4)
The function is decreasing for all real values of x where x < 1.5.
This option is correct.
Since it could be observed from the graph that the function is decreasing for x<1.5.
