Question 799273
solve for x
sin^4x-2sin^2x-1=0
let u=sin^2x
u^2=sin^4x
u^2-2u-1=0
solve for u with quadratic formula:
{{{u = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}
a=1. b=-2, c=-1
ans:
u≈-0.4142(reject)
or
u≈2.4142
..
sin^2x=2.4142
x=±√2.4142≈±1.5537(radians)