X2+10x+2=0 after removing c, what value is added to both sides of the equation.

Can you me find the missing length. i attached an image.

With finding limits of multi variable !

To find the inverse of a number a, one can use the equation f(c) = a-1/c=0 where c is the inverse of a use the secant method of finding roots of equations to find the inverse of a = 2.5 ,er = 0.001%