Question

13. Evaluate f(x) = 12 for the function f(x) = 5(x - 3) + 17. A 2 B-2 C. 62 D. -62

Answer 1

Answer:

Step-by-step explanation:

First, let's rewrite the original function:

ƒ(x) = 5(x – 3) + 17

This could easily be simplified, which might make it easier:

ƒ(x) = 5x – 15 + 17  — distribute the 5 to (x – 3)

ƒ(x) = 5x + 2  — simplify

That looks easier to solve, doesn't it? Now, let's substitute 12 for x and solve for ƒ(12) [this is another way of writing x = 12]

ƒ(12) = 5(12) + 2  — substitute 12 for x

ƒ(12) = 60 + 2  — multiply and simplify

ƒ(12) = 62  — add and simplify

Now, let's prove this method works by substituting 12 for x in the original function:

ƒ(x) = 5(x – 3) + 17 — original function

ƒ(12) = 5(12 – 3) + 17 — substitute 12 for x

ƒ(12) = 5(9) + 17 — here, I subtracted the numbers in the parentheses

ƒ(12) = 45 + 17 — simplify by multiplying 5 and 9

ƒ(12) = 55 + 7 — rewriting to make mental addition easier

ƒ(12) = 60 + 2 — rewriting to make mental addition easier; does this look familiar?

ƒ(12) = 62 — simplifying to find final answer

That's just one way of breaking up the numbers so they're easier to add. You could just use a calculator, but I did this in my head, so…

There's two more ways to use the original function to solve for ƒ(12), and it's these methods:

Method 1

ƒ(x) = 5(x – 3) + 17 — original function

ƒ(12) = 5(12 – 3) + 17 — substitute 12 for x

ƒ(12) = 60 – 15 + 17 — here, I distributed 5 to each term before doing anything else

ƒ(12) = 45 + 17 — simplifying by subtracting 15 from 60

ƒ(12) = 62 — simplifying; we get the same answer

Method 2

ƒ(x) = 5(x – 3) + 17 — original function

ƒ(12) = 5(12 – 3) + 17 — substitute 12 for x

ƒ(12) = 60 – 15 + 17 — here, I distributed 5 to each term before doing anything else

ƒ(12) = 60 + 2 — simplifying by subtracting 15 from 17

ƒ(12) = 62 — simplifying; we get the same answer

What happens every time? We get the same answer, ƒ(12) = 62! To boot, sometimes you can use a rule of three to prove something true: if something happens 3 times, it will be true. Of course, you probably won't have time to do all this. I did so to help you understand the concept better. By the way, the last two methods don't follow the order of operations, P.E.M.D.A.S. (operations in parentheses; exponents; multiplication; division; addition; subtraction). That's a heads-up in case you get an order of operations question so you don't make a mistake.

I hope this helps you! Have a great day!