34 CHAPTER R Review of Basic Concepts EXAMPLE 9 Measuring Blood Pressure Difference Systolic blood pressure is the maximum pressure produced by each heartbeat. Both low blood pressure and high blood pressure may be cause for medical concern. Therefore, health care professionals are interested in a patient’s “pressure difference from normal,” or Pd. If 120 is considered a normal systolic pressure, then Pd = 0 P - 1200 , where P is the patient’s recorded systolic pressure. Find Pd for a patient with a systolic pressure, P, of 113. SOLUTION Pd = P - 120 = 0 113 - 120 0 Let P = 113. = 0 -7 0 Subtract. = 7 Definition of absolute value S Now Try Exercise 141. EXAMPLE 10 Evaluating Absolute Value Expressions Evaluate each expression for x = -6 and y = 10. (a) 0 2x - 3y 0 (b) 20 x 0 - 0 3y 0 0 xy 0 SOLUTION (a) 0 2x - 3y 0 = 0 21-62 - 31102 0 Substitute: x = -6, y = 10. = 0 -12 - 300 Work inside the absolute value bars. Multiply. = 0 -420 Subtract. = 42 Definition of absolute value (b) 20 x 0 - 0 3y 0 0 xy 0 = 20 -6 0 - 0 31102 0 0 -61102 0 Substitute: x = -6, y = 10. = 2 # 6 - 0 300 0 -600 0 -60 = 6; Multiply. = 12 - 30 60 Multiply; 0 300 = 30, 0 -600 = 60 = -18 60 Subtract. = - 3 10 Write in lowest terms; -a b = - a b S Now Try Exercises 143 and 147. NOTE When applying the rules for order of operations, absolute value bars can act as grouping symbols. See Example 10(b).
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