Intermediate Algebra for College Students (7th Edition)

Does not make sense. Take for example the equation: $x^2 - bx = c$ Adding a negative constant will only affect the constant term $c$, and will not get you closer to completing the square. It will, in fact, give you an equation where you still need to isolate the binomial term. $x^2 - bx -c = c -c$ $x^2 - bx -c = 0$ Instead, what you need to do is to get the square of half the value of the coefficient of the $x$-term, and add this on both sides to complete the square. $x^2 - bx + (\frac{-b}{2})^2= c +(\frac{-b}{2})^2$
Does not make sense. Take for example the equation: $x^2 - bx = c$ Adding a negative constant will only affect the constant term $c$, and will not get you closer to completing the square. It will, in fact, give you an equation where you still need to isolate the binomial term. $x^2 - bx -c = c -c$ $x^2 - bx -c = 0$ Instead, what you need to do is to get the square of half the value of the coefficient of the $x$-term, and add this on both sides to complete the square. $x^2 - bx + (\frac{-b}{2})^2= c +(\frac{-b}{2})^2$