Question

Some of the steps in the derivation of the quadratic formula are shown. Step 4: StartFraction negative 4 a c + b squared Over 4 a EndFraction = a ( x + StartFraction b Over 2 a EndFraction) squared Step 5: (StartFractio.n 1 Over a EndFraction) StartFraction b squared minus 4 a c Over 4 a EndFraction = (StartFraction 1 Over a EndFraction) a (x + StartFraction b Over 2 a EndFraction) squared Step 6: StartFraction b squared minus 4 a c Over 4 a squared EndFraction = ( x + StartFraction b Over 2 a EndFraction) squared Step 7: StartFraction plus or minus StartRoot b squared minus 4 a c EndRoot Over 2 a EndFraction = x + StartFraction b Over 2 a EndFraction Which best explains why the expression plus or minus StartRoot b squared minus 4 a c EndRoot cannot be rewritten as b plus or minus StartRoot negative 4 a c EndRoot during the next step? Negative values, like −4ac, do not have a square root. The ± symbol prevents the square root from being evaluated. The square root of terms separated by addition and subtraction cannot be calculated individually. The entire term b2 − 4ac must be divided by 2a before its square root can be determined.

Answer 1

The reason why we used plus or minus when taking the square root is because; The square root of terms separated by addition and subtraction cannot be calculated individually.

How to use the quadratic formula?

The general formula for a quadratic equation is;

ax² + bx + c = 0

Now, the steps to derive quadratic formula to find the roots of this equation are as follows;

Step 1; Divide both sides of the equation by a to get;

x² + (b/a)x + c/a = 0

Step 2; Transpose the quantity c/a to the right side of the equation to get; x² + (b/a)x =  -c/a

Step 3; Complete the square by adding b²/4a² to both sides of the equation to get; x² + (b/a)x + b²/4a² =  -c/a + b²/4a²

Step 4; Factor the left side and combine the right side to get;

(x + (b/2a))² = (b² - 4ac)/(4a²)

Step 5:  Extract the square-root of both sides of the equation to get;

x + (b/2a) = ±(√(b² - 4ac))/2a

The reason why we used plus or minus when taking the square root is because The square root of terms separated by addition and subtraction cannot be calculated individually.

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