Question

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(16x^2)
= 80x^2
The composition was done in the incorrect order.
The negative sign for f(x) was not included in the calculation.
The coefficient of f(x) was squared incorrectly.
The coefficients should be multiplied and then squared.

Answer 1

The composition was done in the incorrect order.

Correct is:

$f(x)=-4x,\ g(x)=5x^2\\\\\ [f\circ g](x)=-4(5x^2)=-20x^2$