1. 1.4 Rewriting Equations and Formulas

2. In section 1.3, we solved equations with one variable. Many equations involve more than one variable. We will solve such equations for one of its’ variables. Example 1: Solve the following equations for y: a. 11x – 9y = –4 b. 2x + 3y = 25 c. Find x if y = 2,4,6,8,10 xy – x = 4 To make this easier, why not change it to y = ?

3. Real World You are selling two kinds of shirts – one cheap and the other quality. Write an equation with more than one variable that represents the total revenue. You expect to sell 125 of the cheapies for $8. To meet your goal of $1600 in sales, what would you need to charge for the quality shirts if you can sell 50 quality shirts? 60 quality shirts?

4. Common Formulas Distanced = rtd = distance, r = rate, t = time Simple InterestI = PrtI = interest, P = principal, r = rate, t = time TemperatureF = 9/5 C + 32F = degrees Fahrenheit, C = degrees Celsius Area of a triangleA = ½ bhA = area, b = base, h= height Area of a RectangleA = lwA = area, l = length, w = width Perimeter of a Rectangle P = 2l + 2wP = perimeter, l = length, w = width Area of a TrapezoidA = ½ (b + b)hA = area, b = bases, h = height Area of a CircleA = (3.14)r²A = area, r = radius Circumference of a CircleC = 2(3.14)r C = circumference, r= radius

5. Example 2: 1. d=rt a. d = 256 miles and r = 24 mph, what is t? b. d = 412 miles and r = 52 mph, what is t? 2. P = 2l + 2w If the perimeter of a rectangle is 124 cm and one side needs to be 24 cm, what is the length of the other side? 3. F = Solve for C.