5-Minute Check Solve each equation. Check your solution. x/3 = -6 -18

Objective: Solve problems using formulas.

To Solve an Equation means... To isolate the variable it must be by it’s lonesome. (Have a coefficient of positive 1) Ex: x = 5 is solved for x. y = 2x - 1 is solved for y.

Example Suppose a car travels at 55 mi/h for 3 h. How far did it travel? d = rt d = 55 • 3 d = 165 mi Distance

Formula shows the relationship between 2 or more quantities. d = 2r Diameter = 2 x radius d = rt distance = rate • time

Example Use the formula d = 2r to find the radius of a circle that has a diameter of 18 meters. d = 2r Diameter formula. 18 = 2r Substitute 18 for d. 18/2 = 2r/2 Divide each side by 2. A circle with a diameter of 18 meters has a radius of 9 meters. 9 = r

Two – Step Equations To isolate the variable it must be by it’s lonesome. (Have a coefficient of +1)

Solving Multi-Step Equations Ex: x + 9 = 6 5

The DO-UNDO chart Use a chart as a shortcut to answering the questions. DO UNDO ÷5 -9 +9 *5 Follow the steps in the ‘undo’ column to isolate the variable. Ex: x + 9 = 6 5 First subtract 9. x + 9 - 9 = 6 - 9 x = -3 Then multiply by 5. (5) x = -3(5) x = -15

Transforming Equations Containing Only Variables Solve ab – d = c for b. ab – d = c + d +d ab = c + d a a DO UNDO * a + d - d / a

Solve the formula for the area of a triangle for height h. A = ½ h B 2 * *2 B b DO UNDO A = ½ h B * 1/2 / b * b / ½ (*2)

Homework Pg 83 8-18 even For 14-18 use do and undo charts  Look in textbook to find formulas for areas of figures