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Evaluating Functions

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A function is a mapping between an input and output. For example, the function f(x) = 3x – 2 takes an input ‘x’ and output is 3x – 2.

 In other words, we can say that a function is a relation between two variables, in such a way that value of the first variable gives one and only one value for the second variable.

Value of f(x) = 3x – 2 at x = 3 is f(3) = 3(3) – 2 = 9 – 2 = 7

Example: If g(x) = 2x + 1, then what is the value of g(-3)?

g(-3) = 2(-3) + 1 = -6 + 1 = -5

Example: If f(x) = -5x2 + 7, the find f(4).

f(4) = -5(4)2 + 7 = -5(16) + 7 = -80 + 7 = -73

CHECK POINT

  1. If f(x) = -72x, then find f(2).
  2. If h(n) = 2 × 5(n – 3), then what is the value of h(4)?
  3. If f(x) = x3 – 1, the find x if f(x) = 215.
  4. If g(t) = 2t2 – 1, then what is the value of g(5)?
  5. If f(t) = 5t – 1, the find f(-5).
Answer key
  1. 2,401
  2. 10
  3. 6
  4. 49
  5. -26

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