Question

Complete the Square of the quadratic equation in standard form: ax2 + bx + c Treat this like a literal equation where you are solving for x by completing the square. To get started, write the equation in the form: x2 + bx = ?

Answer 1

Answer:

x = [-b ±√(b² - 4ac)]/2a

Step-by-step explanation:

ax² + bx + c = 0

dividing through by a, we have

ax²/a + bx/a + c/a = 0

x² + bx/a + c/a = 0

x² + bx/a = -c/a

we now add th square of half the coefficient of x to both sides, thus

x² + bx/a + (b/2a)² = -c/a +  (b/2a)²

simplifying the left hand side and right hand side, we have

(x + b/2a)² = -c/a + b²/4a²

re-arranging, we have

(x + b/2a)² = b²/4a² - c/a

taking L.C.M of the right hand side, we have

(x + b/2a)² = (b² - 4ac)/4a²

taking square-root of both sides, we have

√(x + b/2a)² = ±√[(b² - 4ac)/4a²]

x + b/2a = ±√(b² - 4ac)/2a

So, x = -b/2a ±√(b² - 4ac)/2a

taking the L.C.M of the right hand side, we have

x = [-b ±√(b² - 4ac)]/2a