Question 84683
If the equation is of the form ax^2 + bx + c = 0, then by formula,

{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}

The given equation is 2x^2 + x - 1 = 0,

where a = 2, b = 1 and c = -1.

So plugging in the above formula,

{{{x = (-1 +- sqrt( 1^2-4*2*(-1) ))/(2*2) }}}

==> {{{x = (-1 +- sqrt( 1+8 ))/(4) }}}

==> {{{x = (-1 +- sqrt( 9 ))/(4) }}}

==> {{{x = (-1 +- 3)/(4) }}}

==> x = (-1+3)/4  and x = (-1-3)/4

==> x = 2/4  and x = -4/4

==> x = 1/2  and x = -1


Good Luck!!!