Solving this problem requires you to use two pieces of mathematical information. The first is the Complex Conjugate Root Theorem (it's in your book), which tells you that for any polynomial with real coefficients, if 7i is a root so is its conjugate, -7i. So at a minimum you have three roots, 1/2, 7i, and -7i. The second piece of information is that when given the roots, use the factored form of a polynomial (it's also in your book):
y = a·(x-r1)(x-r2)(x-r3)... (keep going for as many roots as are given)
where a is a constant and is given in your problem as a = 2, and r1, r2, and r3 are the roots which are 1/2, 7i, and -71. Plug in the values for a, r1, r2, and r3 into the formula for the factored form to get the answer. Multiply it out if you want it in standard form.
