Question 26290
{{{16x^2-80x-12}}}
{{{ 4(4x^2-20x-3) }}}


{{{ 4(4x^2-20x-3) }}}. I cannot see this factorising easily, so resort to the quadratic formula.


{{{x = (-b +- sqrt(b^2 - 4ac))/(2a)}}}
{{{x = (-(-80) +- sqrt((-80)^2 - 4(16)(-12)))/(2(16))}}}
{{{x = (80 +- sqrt(6400 + 768))/(32)}}}
{{{x = (80 +- sqrt(7168))/(32)}}}


Now to try to simplify the square root. Start with an easy pair of factors like 4*1792 and build up to 16*448 etc, until you end up with a primary number... like the 7 below.


{{{x = (80 +- sqrt(1024*7))/(32)}}}
{{{x = (80 +- sqrt(1024)sqrt(7))/(32)}}}
{{{x = (80 +- 32sqrt(7))/(32)}}}
{{{x = (80 + 32sqrt(7))/(32)}}} OR {{{x = (80 - 32sqrt(7))/(32)}}}
{{{x = (2.5 + sqrt(7))}}} OR {{{x = (2.5 - sqrt(7))}}}


jon.