# Suppose that the function T has period 7 and that T(0)=3

Suppose that the function T has period 7 and that T(0)=3.

Explain why T(-30)=T(40)?

Is it normal that teacher just tells you to read stuff in book and then do your homework, without explaining it? She was "teaching" some stupid stuff about graphing f(x)=(x-1)^2 + 2, which they teach you in Alg I and then gives you questions about periodic equations. Last two days one girl and me were the only ones to be able to do the homework. Related Introductory Physics Homework Help News on Phys.org
LeonhardEuler
Gold Member
If a function has a period, that means it repeats. Since the period is seven, that means that T(0)=T(7)=T(14)=... and that T(1)=T(8)=T(15)=.... In general it means that whatever value the function has at "a", it will have the same value at "a+7", "a+14", and so on. Do you see the solution now?

Doc Al
Mentor
What's the meaning of period? If the period is 7 (as given), what can you say about T(x) compared to T(x +7)?

I understand that every 7 the function repeats. But if I go 7 in positive and 7 in negative direction then I should have T(40)=T(-40) or T(30)=T(-30). Or am I missing something?

O damn. I got it. My bad. Thanks for help.

Doc Al
Mentor
You're missing something. Complete this list:
T(-30) = T(-30 + 7) [which is T(-23)] = T(-23 +7) ... and so on...

Shame on me. I calculated that there are 50 numbers between -30 and 40. I guess I'm to pised off.

HallsofIvy