My Math Forum Another functional disfunction

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 November 13th, 2016, 12:20 PM #1 Member   Joined: Nov 2016 From: Ireland Posts: 79 Thanks: 2 Another functional disfunction If r(t) = 2t+3 and s(t) = 7t^2 - t find :- s(r(t)) s(r(t)) = s(2t + 3) = 7(2t + 3)^2 − (2t + 3) <<<{Where is this guy coming from?} = 7(4t^2 + 12t + 9) − (2t + 3) = (28t^2 + 84t + 63) − (2t + 3) = 28t^2 + 82t + 60 I can understand the first (2t + 3)^2 but surely that should cover the function s. Why the need for the -2t + 3? Last edited by Kevineamon; November 13th, 2016 at 12:23 PM.
 November 13th, 2016, 12:53 PM #2 Global Moderator   Joined: Dec 2006 Posts: 18,841 Thanks: 1564 Each "t" in "s(t) = 7t^2 - t" is to be replaced with "2t + 3". Thanks from Kevineamon
 November 13th, 2016, 01:03 PM #3 Member   Joined: Nov 2016 From: Ireland Posts: 79 Thanks: 2 Ahhh well there we go. Thanks Skipjack.

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