The function f(x) varies directly with x, and f(x) = 45 when x = 9.
evaluate f(x) when x= 3.

a=5
b=9
c=15
d=27

Option C = 15

Step-by-step explanation:

In principle when a function f(x) varies directly with x it suggests that any changes in x results in the equivalent changes in f(x). If we have two variables, i.e. y representing f(x) and x representing itself, any increment/decrement in x will result to the same increment/decrement in y by a factor a, thus we can say that y = ax, implying y and x have the same ratio.

In the given question we know that when , which translates as

This tells us that varies by a factor (lets call it) for a given value of .

To find this factor we can just divide 45 with 9 which gives:

Thus the factor here is which finally tells us that

   Eqn (1) our original function.

Since we now know our function we can plug in the value for and solve for as follow:

Looking at the given options in the question we can conclude that the correct answer is Option C = 15

the first one, all those points on the line just make a strait line.

step-by-step explanation: