Questions 75, 76, 77

$1 of 73. f(x) = Vx+ V1 -3x 74. f ( x ) = V 2x + (x2 + x ) 4 80. APPLICATIONS Business and Economics le 75. Total revenue. A total-revenue function is given by R(x) = 1000 V x2 - 0.1x, where R(x) is the total revenue, in thousands of dollars, le. using the from the sale of x items. Find the rate at which total 81. revenue is changing when 20 items have been sold. 76. Total cost. A total-cost function is given by C (x) = 2000(x2+ 2)1/3 + 700, where C(x) is the total cost, in thousands of dollars, of producing x items. Find the rate at which total cost is 82. changing when 20 items have been produced. 77. Total profit. Use the total-cost and total-revenue func- tions in Exercises 75 and 76 to find the rate at which and sold. total profit is changing when x items have been produced 78. Total cost. A company determines that its total cost, in thousands of dollars, for producing x items is 83 hich C (x ) = V5x2 + 60, and it plans to boost production t months from now according to the function x (t) = 20t + 40. How fast will costs be rising 4 months from now? 79. Consumer credit. The total outstanding consumer credit of the United States (in billions of dollars) can be x+2 modeled by the function 84 C(x) = 0.21x4 - 5.92x3 + 50.53x2- 18.92x + 1114.93, * + 5 )+ where x is the number of years since 1995. Dule to