Functions

Algebra Level 1

Given the function f ( x ) = a x + b f(x)=ax+b , and the values f ( − 1 ) = 7 f(-1)=7 and f ( 4 ) = 2 f(4)=2 , find a + b a+b .


The answer is 5.

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Victor Paes Plinio by Victor Paes Plinio , 21, Brazil

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1 solution

Abyoso Hapsoro
Apr 3, 2015
  1. f ( − 1 ) = 7 f(-1) = 7 − a + b = 7 -a + b = 7
  2. f ( 4 ) = 2 f(4)=2 4 a + b = 2 4a + b = 2 Eliminate these two and you get: − 5 a = 5 -5a = 5 , therefore a = − 1 a = -1 . Then, substitute a a into one of the 2 equations and you get b = 6 b = 6 a + b = − 1 + 6 = 5 a + b = -1 + 6 = 5 .
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