Question 2539
in a quadratic equation

ax^2+bx+c = 0
x = (-b + sqrt(b^2-4ac))/2a and (-b - sqrt(b^2-4ac))/2a

so for the quadratic equation
8x^2-x-7 

a=8, b=-1, c=-7

therefore, x = (-(-1) + sqrt((-1)^2 - 4*8*(-7)))/2*8 = (1+sqrt(225))/16 =(1+15)/16=1

and also 
x =  (-(-1) - sqrt((-1)^2 - 4*8*(-7)))/2*8 = (1-sqrt(225))/16 =(1-15)/16=-14/16 = -7/8

so x = 1, -7/8