How do you solve $7x^2 = 21x$ using the quadratic formula?

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Answer 1 · 2016-05-17T06:37:15

The solutions are:
$x = 3$

$x= 0$

$7x^2 = 21x$

$7x^2 - 21x = 0$

The equation is of the form $color(blue)(ax^2+bx+c=0$ where:

$a=7, b=-21, c=0$
(the expression has no constant term)

The Discriminant is given by:

$Delta=b^2-4*a*c$

$= (-21)^2-(4* 7 * 0)$

$= 441$

The solutions are found using the formula
$x=(-b+-sqrtDelta)/(2*a)$

$x = (-(-21)+-sqrt(441))/(2*7) = (21+-21)/14$

$x=(21+21) / 14 = 42/14 = 3$

$x=(21-21) / 14 = 0/14 = 0$

How do you solve 7x^2 = 21x7x^2 = 21x using the quadratic formula?