Zaymiey

📐 Mathematics  ·  Complex Numbers and Quadratic Equations  ·  JEE

The equation x² - 2px + q = 0 has two real roots r, s. For r² + s² to be minimized, what condition on p,q?

Answer: p² = q.

  • A p = 0
  • B p² = q
  • C q must be maximum
  • D p must equal q

Correct answer: B. p² = q

Explanation: r² + s² = (r+s)² - 2rs = 4p² - 2q. Minimize means dL/dq = -2 < 0 so max q, but constraint D = 4p² - 4q ≥ 0 means q ≤ p². Minimum r²+s² at boundary q = p².

Argand Plane: z = a + ibReImz = a+iba (real part)b (imaginary part)θ = arg(z)|z| = length of the vector OZ = √(a²+b²); θ = angle OZ makes with the positive real axis

A complex number z = a+ib is plotted as a point (or vector from the origin) on the Argand plane, with the real part along the horizontal axis and the imaginary part along the vertical; its modulus |z| is the vector's length, and its argument θ is the angle from the positive real axis.

Concept context

Complex numbers in a+ib form, modulus, argument, polar form, cube roots of unity, and quadratic equations with complex roots

Read the full Complex Numbers and Quadratic Equations notes →