Question

SECTION -BITWO MARK QUESTIONS)
Q(21) if "a" and "b" are roots of x^2+x+1=0 then value of (a+ b) can be
Written as
(a) i/2
(b) 1/2
(c)-1+3i)/2
(d) a +b-ab=0​

Answer 1

Answer:

(d) a + b - ab = 0

Step-by-step explanation:

x² + x + 1 = 0

D = 1² - 4 = - 3

$x_{1}$ = [- 1 - √(- 3)] / 2 = [- 1 - i√3] / 2

$x_{2}$ = [- 1 + i√3] / 2

$x_{1}$ + $x_{2}$ = [- 1 - i√3 + - 1 + i√3 ] / 2 = - 2 / 2 = - 1

$x_{1}$$x_{2}$ = (- 1 - i√3)(- 1 + i√3) / 4 = [(- 1)² - (i√3)²] / 4 = 1

a + b = - 1 and ab = 1 ⇒ a + b - ab = 0