For \( f(x)=5-x \) and \( g(x)=4 x^{2}+x+7 \), find the following functions. a. \( (f \circ g)(x) ; b .(g \circ f)(x) ; c .(f \circ g)(2) ; d .(g \circ f)(2) \) a. \( (f \circ g)(x)=\square \) (Simplify your answer.)
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Bonus Knowledge
To find the composed functions, we’ll start with \( (f \circ g)(x) \) and \( (g \circ f)(x) \). a. For \( (f \circ g)(x) \): \[ (f \circ g)(x) = f(g(x)) = f(4x^2 + x + 7) \] Substituting \( g(x) \) into \( f(x) \): \[ = 5 - (4x^2 + x + 7) = 5 - 4x^2 - x - 7 = -4x^2 - x - 2 \] So, \[ (f \circ g)(x) = -4x^2 - x - 2 \] b. For \( (g \circ f)(x) \): \[ (g \circ f)(x) = g(f(x)) = g(5 - x) \] Substituting \( f(x) \) into \( g(x) \): \[ = 4(5 - x)^2 + (5 - x) + 7 \] Now simplifying \( (5-x)^2 \): \[ = 25 - 10x + x^2 \] So, \[ g(f(x)) = 4(25 - 10x + x^2) + (5 - x) + 7 = 100 - 40x + 4x^2 + 5 - x + 7 = 4x^2 - 41x + 112 \] Thus, \[ (g \circ f)(x) = 4x^2 - 41x + 112 \] Now for the specific evaluations. c. Calculating \( (f \circ g)(2) \): \[ (f \circ g)(2) = -4(2^2) - 2 - 2 = -4(4) - 2 - 2 = -16 - 2 - 2 = -20 \] So, \[ (f \circ g)(2) = -20 \] d. Calculating \( (g \circ f)(2) \): \[ (g \circ f)(2) = 4(2)^2 - 41(2) + 112 = 4(4) - 82 + 112 = 16 - 82 + 112 = 46 \] So, \[ (g \circ f)(2) = 46 \] In summary: a. \( (f \circ g)(x) = -4x^2 - x - 2 \) b. \( (g \circ f)(x) = 4x^2 - 41x + 112 \) c. \( (f \circ g)(2) = -20 \) d. \( (g \circ f)(2) = 46 \)
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