For this reason, if we know the roots (in this case, 3 and -4), we can write the factored form of the quadratic:
(x-3)(x+4) = 0 <--- notice the signs are oposite of their roots.
2) x^2 + 7x + c ... let's pretend like we're completing the square to find the value for c:
x^2 + 7x ... taking 7, dividing it by 2, then squaring that, we get, 49/4 ... if we were completing the sqare, we would add and subtract 49/4 and then use the 49/4 to factor x^2 + 7x + c, therefore:
c = 49/4