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1.4 Rewriting Equations and Formulas Many equations involve more than one variable. It is often necessary to rewrite an equation or formula by isolating a single variable. Ex: Ex: Solve the following equation for y. 11x − 9y = −4 Ex: Ex: Find the value of y when x = – 4 and x = 2. (Hint: Solve for y first.) xy – x = 4 Ex: Ex: Solve each formula for the underlined variable. a.) P = 2l + 2w (Perimeter of a rectangle) b.) A = π r 2 (Area of a circle) c.) F = 9 C + 32 5 More formulas that might come in handy… (Temperature) Try the following… Find the radius of a circle with a circumference of 25 feet. Solve the formula P = 2l + 2w for l. Then find the length of a rectangle with a width of 7 inches and a perimeter of 30 inches. Solve the formula A = lw for w. Then find the width of a rectangle with a length of 16 meters and an area of 40 square meters.