Complex Numbers And Quadratic Equations

If the sum of first n positive integer is 1/(5) times the sume of their squares, then n equals

The equation of the normal to the ellipse at is

If every pair from among the equations x²+px+qr=0, x²+qx+rp=0 and x²+rx+pq=0 has a common root then the product of three common roots is

If z and are non-zero complex numbers such that and , then is equal to