How do you solve $q^2-21q=-20$ ?

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Answer 1 · 2016-04-02T17:33:57

The solutions are:

$color(green)(q = 20$

$color(green)(q = 1$

$q^2 - 21 q = -20$

$q^2 - 21 q + 20 = 0$

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

$a=1, b=-21, c=20$

The Discriminant is given by:

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

$= (-21)^2-(4*1 * 20)$

$= 441 - 80 =361$

The solutions are normally found using the formula:

$q=(-b+-sqrtDelta)/(2*a)$

$q = (-( - 21)+-sqrt(361))/(2*1) = ((21+- 19))/2$

$q= ((21+ 19))/2 = 40 / 2 = 20$

$q= ((21 - 19))/2 = 2 / 2 = 1$

How do you solve q^2-21q=-20q^2-21q=-20?