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College Mathematics

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Examples and Solutions

Interest: You plan to put away \$50.00 every month in the bank at a rate of 8% compounded monthly. How much will you have at the end of 5 years?

This is a problem on Annuity. It is a sequence of equal deposits or payments toward an account made at equal time intervals. The Amount of the Annuity will be the total at the end of the period including all interests. The amount of an annuity compounded annually is given by:
P{(1 + i)N - 1}
V =   --------------------
i
where P in dollars is the invested amount at the end of each year up to N years at interest rate i. If the interest is compounded n times each year and deposits made every compounding period, then
P{(1 + i/n)nN - 1}

V =  ------------------------                                                                                      i/n

the formula to be used in this example. Substituting the values, we then have

###### 50{(1 + 0.08/12)(12X5) - 1}              50{(1 + 0.006667)60 - 1}                                   V  =   --------------------------------------     =      ---------------------------------                                                             0.08/12                                           0.006667

50{(1.006667)60 - 1}               50{1.489875 - 1}
=    ------------------------------    =        -----------------------
0.006667                                0.006667

=   50 x 0.489875      =    24.49375
0.006667                               0.00667
=   3673.87

Approx.  \$3,673.87

Decay: The value of a certain machine has an annual decay factor of 0.75. If the machine is worth \$10,000 after 5 years, what was the original value of the machine?

The machine will decay exponentially as in radioactive elements.
Therefore, applying the Exponential Decay Formula:
y = abx
Where y = the final amount, a = the original value, b the decay factor,
and x the time in years.
By substitution, 10,000 = (a)(0.75)5
10,000 = (a)(0.2373)
a =  10000
0.2373
=  42,140.75

Inequalities: Solve 3y + 4 > 2(y + 3) + y
3y + 4 - 4 > 2y + 6 + y - 4  (Subtracting 4 from each side.)
3y + 0 > 2y + y + 6 - 4  (Grouping like terms.)
3y > 3y + 2
3y - 3y > 3y -3y + 2  (Subtracting 3y from both sides.)
0 > 0 + 2

Answer: Since y is eliminated, there are no values to display

 Trigonometry: Solve the equation, 2sin²θ - sinθ = 0                       This is a Quadratic Equation as in 2x² - x = 0                                     By factorization, Sinθ(2sinθ - 1) = 0                                              So, sinθ = 0 and 2sinθ - 1 = 0              When sinθ = 0, angle θ = 0º, 180º and 360º   Also, for 2sinθ - 1 = 0,  sinθ = 0.5, Angle θ = 30º and 150º   Answer: Solutions of θ are 0º, 30º, 150º, 180º and 360º.   Radicals: Simplify √50 + √2 - 2√18 + √8.      50 + √2 - 2√18 + √8 = √(25 x 2) + √2 - 2√(9 x 2) + √(4 x 2)                                          = 5√2 + √2 - (2 x 3)√2 + 2√2                                           = 6√2 - 6√2 + 2√2                                           = 2√2                            Answer:  2√2 Series: The fourth term of a Geometric Progression (G.P.) is -6 and the seventh term is 48. What are the first three terms of the progression?                     4th Term:  ar3 = -6  - equation 1                      7th Term: ar6 = 48  - equation 2  Dividing equation 2 by equation 1:                                          ar6 = 48                                   ÷   ar3 = -6                                            r3 = -8                                             r  = -2  Substituting the value of r in any equation, say eq.2 to find a:                                      a(-2)  =  -6                                         -8a  =  -6                                            a  =  -6/-8  =  ¾  First Term of the GP is ¾  Second Term is ¾ X -2 = -6/4 = -1½ and Third Term is -1½ X -2 = 6/2 = 3  First three terms are ¾,  -1½,  3

 Functions: Given the function f(x) = 2x² - 5x + 3.  Find the values of x and draw a graph of the function.                    Let y = f(x) = 2x² - 5x + 3                   If y = f(x)                         Then y = 2x² - 5x + 3                                                                  y = (x - 1)(2x - 3) by factorization                 When y = 0, x - 1 = 0 and 2x - 3 = 0                     When x - 1 = 0, x = 1                        When 2x - 3 = 0, x = 3/2 = 1½  Values of x are 1 and 1½ The solutions are the intercepts of the graph on the x axis, 1 and 1½.