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If g(x) = x + 1 and f(x + (1)/(x)) = x2 + (1)/(x2), what is f(g(2))?

Mathematics

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Answer

B\text{B}

Graph of g(x) = x + 1

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Key points of g(x) = x + 1
Pointxy
x-intercept−10
y-intercept01

Step-by-step solution

4 steps
  1. Evaluate g(2)g(2).

    The function g(x)g(x) is given by g(x)=x+1g(x) = x + 1.
    Substitute x=2x=2 into g(x)g(x):

    g(2)=2+1=3g(2) = 2 + 1 = 3
  2. Express f(x+1x)f(x + \frac{1}{x}) in a simpler form.

    The function ff is defined by f(x+1x)=x2+1x2f(x + \frac{1}{x}) = x^2 + \frac{1}{x^2}.
    We know the algebraic identity (a+b)2=a2+2ab+b2(a+b)^2 = a^2 + 2ab + b^2.
    Let a=xa=x and b=1xb=\frac{1}{x}. Then:

    (x+1x)2=x2+2⋅x⋅1x+(1x)2\left(x + \frac{1}{x}\right)^2 = x^2 + 2 \cdot x \cdot \frac{1}{x} + \left(\frac{1}{x}\right)^2 (x+1x)2=x2+2+1x2\left(x + \frac{1}{x}\right)^2 = x^2 + 2 + \frac{1}{x^2}

    Rearranging this, we get:

    x2+1x2=(x+1x)2−2x^2 + \frac{1}{x^2} = \left(x + \frac{1}{x}\right)^2 - 2

    So, we can rewrite the definition of ff as:

    f(x+1x)=(x+1x)2−2f\left(x + \frac{1}{x}\right) = \left(x + \frac{1}{x}\right)^2 - 2

    Let u=x+1xu = x + \frac{1}{x}. Then the function ff can be written as f(u)=u2−2f(u) = u^2 - 2.

  3. Calculate f(g(2))f(g(2)).

    From Step 1, we found g(2)=3g(2) = 3.
    Now we need to find f(3)f(3). Using the simplified form of f(u)f(u) from Step 2:

    f(3)=(3)2−2f(3) = (3)^2 - 2 f(3)=9−2f(3) = 9 - 2 f(3)=7f(3) = 7
  4. Select the correct option.

    The calculated value is 7, which corresponds to option (B).

    The final answer is B\text{B}

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