Question

(i) x4 - 2x2 - 3 = 0​

Answer 1

${\huge{\underbrace{\rm{Answer\checkmark}}}}$

$\mapsto \rm \: {x}^{4} - 2 {x}^{2} - 3 = 0$

$\rm \longrightarrow \: let \: \: \: \: \: \: \: \: \: \: {x}^{2} = y$

$\mapsto \rm \: {y}^{2} - 2y - 3 = 0$

$\mapsto \rm \: {y}^{2} + y - 3y - 3 = 0$

$\mapsto \rm \: y(y + 1) - 3(y + 1) = 0$

$\mapsto \rm \: (y - 3)(y + 1) = 0$

$\mapsto \rm \: y = 3 \\ \rm \: or \\ \rm \: y = - 1$

$\mapsto \rm \: x = + \sqrt{3} \: or \: - \sqrt{3}$

$\mapsto \rm \: x = \sqrt{ - 1} which \: is \: imaginary$

$\star \: \boxed{ \rm{x = \sqrt{3} \: or \: - \sqrt{3} }}$

Answer 2

Ghmicromax

Thanks for answer