When f(x)=-7x^2+7x+2=0, we can write: 7x^2-7x-2 and use the quadratic formula for finding the roots, which are the zeroes of the function. x=(7+sqrt(49+56))/14=(7+sqrt(105))/14. To get an approximate answer we can approximate to sqrt(105) and go for sqrt(100)=10. So the approximate roots are (7+10)/14=17/14 and -3/14, or 1.2 and -0.2. If we substitute either of these values we get f(x)=0.32 (remember we reversed the plus and minus signs at the beginning to make the quadratic slightly simpler).