Question

Cedaric completed the square for the quadratic expression 5x2 - 40x + 15, as shown.Step 1: 5(x2 -8x + 3)Step 2: 5(x2- 8x + 16 - 16 + 3)Step 3: 5((x + 4)2 -16 + 3)Step 4: 5((x + 4)2 - 13)Step 5: 5(x + 4)2 - 65What mistake, if any, did Cedric make?

Answer 1

In step 3, he incorrectly wrote the square as (x + 4)². He should have written (x - 4)²

Step-by-step explanation

When he completed the square, he factored out 5 correctly. Then he found that the second term of the binomial was 4, so he added and subtracted the square of 4, which is 16. But in the next step, he made a mistake with the sign,

Instead of writing (x - 4)², he wrote (x + 4)².