Let f(x) = –4x and g(x) = 5x2. Andrew finds the composition [f o g](x) as shown below. What error did Andrew make?= 5(–4x)2 = 5(16x2) = 80x2

The composition [f o g](x) means apply g first, then f. Since g(x) = 5x² and f(x) = −4x, the result is f(g(x)) = −4(5x²) = −20x². Andrew instead substituted f(x) into g, calculating g(f(x)), so he used the functions in the incorrect order.

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