Question

Difficulty: MediumEvaluating Algebraic Expressions
An algebraic function F(a,b)F(a, b) is defined as:
F(a,b)=a2−3bab−1+2F(a, b) = \frac{a^2 - 3b}{a b^{-1} + 2}

The values for variables aa and bb are given in the table below:

VariableValue
aa−4-4
bb−12-\frac{1}{2}

What is the value of F(a,b)F(a, b) for these given values?

  1. A
    −2920-\frac{29}{20}
  2. B
    2920\frac{29}{20}
  3. 74\frac{7}{4}Answer
  4. D
    358\frac{35}{8}
  5. E
    −3512-\frac{35}{12}

Answer

The value of F(a,b)F(a, b) is 74\frac{7}{4}.
Substituting a=−4a = -4 and b=−1/2b = -1/2 into the expression gives a numerator of (−4)2−3(−1/2)=16+3/2=35/2(-4)^2 - 3(-1/2) = 16 + 3/2 = 35/2 and a denominator of (−4)(−2)+2=8+2=10(-4)(-2) + 2 = 8 + 2 = 10. Dividing 35/235/2 by 1010 simplifies to 35/2035/20, which equals 7/47/4.

Step-by-Step Solution

1
Evaluate the reciprocal term b−1b^{-1}
b−1=(−12)−1=−2b^{-1} = \left(-\frac{1}{2}\right)^{-1} = -2
A negative exponent indicates taking the reciprocal of the base.
2
Evaluate the numerator a2−3ba^2 - 3b
(-4)^2 - 3\left(-\frac{1}{2}\right) = 16 + \frac{3}{2} = \frac{35}{2}
Squaring a negative number yields a positive value ((−4)2=16(-4)^2 = 16), and subtracting a negative value is equivalent to addition.
3
Evaluate the denominator ab−1+2a b^{-1} + 2
(-4)(-2) + 2 = 8 + 2 = 10
Multiplying two negative numbers yields a positive product.
4
Divide the numerator by the denominator and simplify
35210=3520=74\frac{\frac{35}{2}}{10} = \frac{35}{20} = \frac{7}{4}
Dividing 352\frac{35}{2} by 1010 gives 3520\frac{35}{20}, which simplifies to 74\frac{7}{4} when dividing both numerator and denominator by 55.

Key Concept

Evaluating algebraic expressions with negative numbers, fractions, and negative exponents.
Estimated Time:1m 30s
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