Math Problem Statement

Let f(x) = -2x^2 - 2x - 4. Let g(x) = -x - 5. Find the following: (a) f(5) + g(5), (b) f(7) * g(7), (c) f(g(4)), (d) g(f(5))

Solution

Let's solve the given problem step by step.

The functions provided are: f(x)=2x22x4f(x) = -2x^2 - 2x - 4 g(x)=x5g(x) = -x - 5

(a) f(5)+g(5)=74f(5) + g(5) = -74

Let's verify this first:

  1. Calculate f(5)f(5): f(5)=2(5)22(5)4=2(25)104=50104=64f(5) = -2(5)^2 - 2(5) - 4 = -2(25) - 10 - 4 = -50 - 10 - 4 = -64

  2. Calculate g(5)g(5): g(5)=(5)5=55=10g(5) = -(5) - 5 = -5 - 5 = -10

  3. Sum f(5)+g(5)f(5) + g(5): f(5)+g(5)=64+(10)=74f(5) + g(5) = -64 + (-10) = -74 The result matches the given answer of 74-74.

(b) f(7)g(7)=1392f(7) \cdot g(7) = 1392

Let's verify this:

  1. Calculate f(7)f(7): f(7)=2(7)22(7)4=2(49)144=98144=116f(7) = -2(7)^2 - 2(7) - 4 = -2(49) - 14 - 4 = -98 - 14 - 4 = -116

  2. Calculate g(7)g(7): g(7)=(7)5=75=12g(7) = -(7) - 5 = -7 - 5 = -12

  3. Product f(7)g(7)f(7) \cdot g(7): f(7)g(7)=116×12=1392f(7) \cdot g(7) = -116 \times -12 = 1392 The result matches the given answer of 1392.

(c) f(g(4))=?f(g(4)) = ?

Let's find this:

  1. Calculate g(4)g(4): g(4)=(4)5=45=9g(4) = -(4) - 5 = -4 - 5 = -9

  2. Calculate f(g(4))=f(9)f(g(4)) = f(-9): f(9)=2(9)22(9)4=2(81)+184=162+184=148f(-9) = -2(-9)^2 - 2(-9) - 4 = -2(81) + 18 - 4 = -162 + 18 - 4 = -148 So, f(g(4))=148f(g(4)) = -148.

(d) g(f(5))=59g(f(5)) = 59

Let's find this:

  1. We already calculated f(5)f(5) earlier: f(5)=64f(5) = -64

  2. Calculate g(f(5))=g(64)g(f(5)) = g(-64): g(64)=(64)5=645=59g(-64) = -(-64) - 5 = 64 - 5 = 59 This matches the given answer of 59.

Summary:

  • (a) f(5)+g(5)=74f(5) + g(5) = -74
  • (b) f(7)g(7)=1392f(7) \cdot g(7) = 1392
  • (c) f(g(4))=148f(g(4)) = -148
  • (d) g(f(5))=59g(f(5)) = 59

Would you like further details or have any questions? Here are some related questions you might consider:

  1. What would be f(g(2))f(g(2))?
  2. How do the graphs of f(x)f(x) and g(x)g(x) compare?
  3. What is the derivative of f(x)f(x)?
  4. How would you solve f(x)=0f(x) = 0?
  5. What would happen if you change g(x)g(x) to a different linear function?

Tip: When substituting values into functions, always perform the operations step by step to avoid errors.

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Math Problem Analysis

Mathematical Concepts

Functions
Quadratic Functions
Linear Functions

Formulas

f(x) = -2x^2 - 2x - 4
g(x) = -x - 5
f(a) + g(a)
f(a) * g(a)
f(g(a))
g(f(a))

Theorems

-

Suitable Grade Level

Grade 9-10