DERIVING THE QUADRATIC FORMULA

ax2 + bx + c = 0

Subtract c from both sides of the equation.

ax2 + bx = -c

Divide both sides by the coefficient of x2.

x2 + (b/a)x = -c/a

Divide the coefficient of x by 2, square it, then add to both sides.
Note: This makes a perfect square on the left side.

x2 + (b/a)x + b2/4a2 = -c/a + b2/4a2

Simplify the left side into a square.

(x + b/2a)2 = -c/a + b2/4a2

Simplify the right side by finding the lowest common denominator.

(x + b/2a)2 = -4ac/4a2 + b2/4a2

Add the fractions on the right.

(x + b/2a)2 = (b2 - 4ac)/4a2

Take the square root of both sides.
Note: The term +/-sqrt = plus or minus the square root of.

x + b/2a = +/-sqrt(b2 - 4ac)/2a

Subtract b/2a from both sides and simplify.

x = [-b +/-sqrt(b2 - 4ac)]/2a

Do you understand my child?

AN EXAMPLE USING THE QUADRATIC FORMULA

If...

2x2 + 3x + 22 = 49

Then...

2x2 + 3x + (-27) = 0

Using the quadratic formula...

x = [-3 +/-sqrt(32 - 4(2)(-27))]/[2(2)]

x = [-3 +/-sqrt(225)]/4

x = -3/4 +/-(15/4)

Therefore...

x = 3 or x = -4.5

PRINTER FRIENDLY

This tutorial created and designed by
Curtis Lee Hall

www.InTheBeginning.com

This webpage is dedicated to
Jodi
The Great Mathematician of Bates Hollow.
Truly a very precious spirit, a brilliant and beautiful soul.
(1Peter 3:4)

Intriguing - (adjective) causing a desire to know more; mysterious.

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My Father's House Ministries
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