Kevin's work for deriving the equation of a circle is shown below. x2 + 4x = - (y2 - 20) step 1 x2 + 4x = - y2 + 20 step 2 x2 + 4x + 4 = - y2 + 20 - 4 step 3 (x + 2) 2 = - y2 + 20 - 4 step 4 (x + 2) 2 + y2 = 16 in which step did he make an error in his work

We have the following equation:

x2 + 4x = - (y2 - 20)

Let's review step by step:

step 1:

x2 + 4x = - y2 + 20

Answer: OK

step 2:

x2 + 4x + 4 = - y2 + 20 - 4

Answer: Wrong

The correct step is:

x2 + 4x - 4 = - y2 + 20 - 4

Or equivalently:

x2 + 4x + 4 = - y2 + 20 + 4

Answer:

he did make an error in his work in step 2