Answer :
You can use z = x², then rewrite the equation as
4z²-21z+20 = 0
This factors as
(4z-5)(z-4) = 0
so has solutions
z = 5/4, 4
The solutions for x are then
x = ±√z = {-2, -(√5)/2, (√5)/2, 2}
4z²-21z+20 = 0
This factors as
(4z-5)(z-4) = 0
so has solutions
z = 5/4, 4
The solutions for x are then
x = ±√z = {-2, -(√5)/2, (√5)/2, 2}
