sin(x) - cos(x) = 0
[ sin(x) - cos(x) ]2 = 02 ( square both sides
sin2(x) - 2sin(x)cos(x) + cos2(x) = 0
sin2(x) + cos2(x) - 2sin(x)cos(x) = 0 ( rearrange )
1 - 2sin(x)cos(x) = 0 ( sin2(x) + cos2(x) = 1
- 2sin(x)cos(x) = -1
2sin(x)cos(x) = 1
sin(2x) = 1 ( sin(2x) = 2sin(x)cos(x) )
2x = sin-1(1)
2x = pi/2
x = pi/4 ( principal root; extend to get the other roots )