Jesset C.
asked • 04/22/20PLEASE help me! I need to know if this is correct!!!
Find fg(7) if f(x) = x + 4; D = {Reals} and g(x )= x2+ 4; D = {Positive integers}.
(A) 583
(B) 64
(C) 125
(D) ∅
(E) None of the above
For this I got; (A) 583. Is this correct?
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1 Expert Answer
Rafael E. answered • 04/22/20
Tutor
New to Wyzant
Math Tutoring
Yes it is correct. A)583
fg(x) = f(x)g(x)
fg(x) = (x+4)(x^2+4)
fg(x) = x^3+4x+4x^2+16 = x^3+4x^2+4x+16
fg(7) = (7)^3+4(7)^2+4(7)+16 = 583
Jesset C.
Thank you so much for answering!
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04/22/20
Stanton D.
Just to be clear Jesset: There are two **different** things that might be meant by fg(x). Usually, as the comment indicated, f(g(x)) is sought; that would be ((7^2+4)+4) or 57. If f(x)*g(x) is sought, then Rafael's solution is correct. Functions, which are a type of operation, are considered to be different entities than mere variables, so fg for functions f and g isn't decoded the same way as fg for the two variables f and g.
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04/22/20
Dmitry B.
Good point, I got 57 too and was confused for a second.
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04/23/20
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Ajay S.
To clarify, are you asking for f(g(7))?04/22/20