# Video: US-SAT04S3-Q04-832171082847

If π(π₯) = 5 + 3π₯, which of the following is equivalent to π(β3π₯)? [A] 5 β 9π₯Β² [B] 5 β 3π₯ [C] 5 β 9π₯ [D] 5 + 3π₯Β²

01:20

### Video Transcript

If π of π₯ equals five plus three π₯, which of the following is equivalent to π of negative three π₯?

Weβre starting out with π of π₯ equals five plus three π₯. And we need to plug in negative three π₯ for the π₯-value. This means that anywhere in our function where π₯ shows up we need to replace it with negative three π₯. After we do that, we can simplify the second function, bring down the five. We can multiply three by negative three, which gives negative nine and thatβs been multiplied by π₯.

We could also think of it another way. We could think of it as multiplying the π₯ thatβs there by negative three. And in that case, every place we see π₯, we would need to multiply that π₯ by negative three. The expression would then be three times negative three times π₯. And that simplifies to negative nine π₯.

The only answer choice that reflects this expression is c five minus nine π₯.