<p>Two solutions of x^2-9x+c=0 are complex conjugate, which of the following describes all possible values of C</p>
<p>1.c=0
2.c=is not zero
3.c>81/4
4.c>81
5.c>9</p>
<p>Can someone explain the reason behind this? thank you so much!</p>
<p>Well ok, if solutions are “complex conjugates,” that means they’re gonna be imaginary. So when you do the quadratic formula, (b^2-4ac) should end up negative so you’ll end up with imaginary numbers when you find the square root. They give you b, which is -9. (-9)^2 = 81. a is 1, so you have 81-4c, and you wanna make that negative. Therefore c has to be greater than 81/4. 3 is the answer.</p>
<p>Thank you! :)</p>