Question

If a + ib is the conjugate of 5 + 11i then a + b = ?
1. 6
2. -6
3. 5
4. -5

Answer 1

Correct Answer - Option 2 : -6

CONCEPT:

• If z = x + iy then conjugate of z is given by \(\bar z = x - iy\)
• If x + iy = a + ib then x = a and y = b.

CALCULATION:

Given: a + ib is the conjugate of 5 + 11i

As we know that, if z = x + iy then conjugate of z is given by \(\bar z = x - iy\)

So, the conjugate of 5 + 11i is 5 - 11i

⇒ a + ib = 5 - 11i

As we know that, x + iy = a + ib then x = a and y = b.

⇒ a = 5 and b = - 11.

⇒ a + b = - 6

Hence, correct option is 2.