68. y' = -9*8*x^7 - 6/5 * 5 * x^4 = -72*x^7 - 6*x^4
69. y' = -5*4*x^3 + 7/6 * 6 * x^5 = -20*x^3 + 7*x^5
70. y' = -5/4 * 4 * x^3 + 3 * 2 * x - 2 = -5*x^3 + 6*x - 2
71. y' = -7/6*6*x^5 + 5*4*x^3 = -7*x^5 + 20*x^3
72. y' = 3 -5cosx, y'(Pi/2) = 3 - 5cos(Pi/2) = 3-0 = 3
73. y' = 7 - sqrt(3)cosx, y'(Pi) = 7 - sqrt(3)cos(Pi) = 7 - sqrt(3)*(-1) = 7 + sqrt(3)
74. y' = -2sinx-6x, y'(0) = -2sin0-6*0 = 0
75. y'=4/cos^2(x) - 30x^5, y' = 4/cos^2(0) - 30*0 = 4
76. y' = 5x^4 + 8x^3 + 3x^2, y'(1) = 5 + 8 + 3 = 16