Question 729964
for all such problems that match with following pattern just follow the procedure and that will easily solve!

pattern: {{{ax^2+bx+c}}}
step 1) determine each value from your equation:
in this  case 
{{{a=-1}}}   {{{b=8}}}   {{{c=-7}}} 

step 2) calculate value D as {{{D= b^2-4ac}}}
in this case
 {{{8^2-4*(-1)*(-7)=64-28=36}}

step 3) if the value of "D" is negative you don't have any answer, that meanes no number can make your eq. value equall to zero "we call it impossible soituation"
in this caseh
 {{{D=36}}} so you would have answer follow to next step to find out.

step4) the answer of this equation would be as follow:
(1) {{{(-b+sqrt(D))/(2a)}}} in this case {{{(-8+sqrt(36))/(2)=-1}}} 
(2) {{{(-b-sqrt(D))/(2a)}}} In this case{{{(-8-sqrt(36))/(2)=-7}}} 

it is obvious that if the value of "D" get equal to zero two answer would be the same as  {{{(-b/2a)}}} 
 
Good Luck