If, in a quadratic equation, the values of a and c have opposite signs, the solutions of the equation are real numbers.

Ax²+bx+c=0 , a>0, c<0 (or a<0, c>0)
D=b²-4ac ≥ 0 always will be positive
because negative*positive = negative, 
a*c -negative, so (-4ac) positive 
So,
If, in a quadratic equation, the values of a and c have opposite signs, the solutions of the equation are real numbers. 
True