Question

The steps for deriving the Quadratic formular are shown. Which best choose for the missing reason?

Answer 1

In the part inside the yellow circle, we multiplied by 1 the term -c/a, that is

`-(c)/(a)=-(c)/(a)*1=-(c)/(a)((4a)/(4a))=-(4ac)/(4a^2)`

where 1 was written as 4a/4a.

Since we must add this result to

`(b^2)/(4a^2)`

the answer is option C, change to LCD ( Least Common Denominator) because both terms must have the same denominator, which is 4a^2.