Mark M. answered 09/19/19
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Average rate of change = [f(2+h) - f(2)] / h = [5(2+h)2 + 8 - (5(2)2 + 8)] / (2+h - 2)
= [5(4 + 4h + h2) - 20] / h = (20h + 5h2) / h = h(20 + 5h) / h = 20 + 5h