Answer:
Luis didn't solve the question properly.
Line 4 is not correct.
Explanation:
We have given a quadratic equation.
-x²+10-21 = y
The question is solved in given pic.
The quadratic formula is applied to given equation.
Line 4 is not correct because √16 ≠ √4
Line 4 : x = -10±4 / (-2)
x = -10+4 / (-2) ; x = -10-4 / (-2)
x = -6/-2 ; x = -14/-2
x = 3 ; x = 7 which is correct answer.
Luis didn't solve the question properly.
Line 4 is not correct.