Quadratic equation

When I solve the quadratic equation x^2+10x1200=0 using factorization I am getting roots 30,40 but on solving using discriminant formula I am getting discriminant method b^24ac= (10)^2  4×1×1200=4200 I am getting negative root inside square root that means complex roots of equation x^2+10x+1200 should be there but using factorisation I am getting real roots what is this I am confused????

@Bhanu
You missed one negative sign.