Q.

Let S be the set of all complex numbers z satisfying z2+z+1=1 . Then which of the following  statements is/are TRUE ?

see full answer

Start JEE / NEET / Foundation preparation at rupees 99/day !!

21% of IItians & 23% of AIIMS delhi doctors are from Sri Chaitanya institute !!
An Intiative by Sri Chaitanya

a

z+12≤12 for all z∈S

b

|z|≤2 for all z∈S

c

Z+12≥12 for all z∈S

d

The set S has exactly four elements

answer is B.

(Unlock A.I Detailed Solution for FREE)

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Detailed Solution

z2+z+1=1⇒ z+122+34=1⇒1=z+122+34≤z+122+34⇒ 1≤z+122+34 ⇒z+122≥14⇒z+12≥12 also z2+z+1=1≥∥z2+z|−1|     sincez1-z2≤ z1+z2 ⇒z2+z−1≤1⇒z2+z≤2⇒∥z2|−|z||≤z2+z≤2⇒r2−r≤2     where r=z ⇒r2-r≤2⇒r2-r-2≤0⇒r-2r+1≤0⇒r-2≤0⇒ r=|z|≤2;∀z∈S Also we can always find root of the equation z2+z+1=eiθ;∀θ∈R Hence set 'S' is infinite
Watch 3-min video & get full concept clarity
score_test_img

Get Expert Academic Guidance – Connect with a Counselor Today!

whats app icon