:: if 4-5i is a zero of a quadratic function with real coefficients, then is also a zero. (simplify your answer. type your answer in the form a+bi).

Answer is 4+5i

The reason is that if you have a zero that is imaginary number, than its conjugate value is also a zero of that function. Conjugate value of imaginary number you get simply when changing sign of imaginary part of imaginary number to opposite. in this case imaginary part is -5i so its conjugate value is +5i..

The answer is why would a teacher ask that