tolong bantu jawab ya

2tanx/(1 - tan²x) - 5 = 0
(tanx + tanx)/(1 - tan²x) = 5
tan(2x) = 5

cos²x - sin²x = cos(2x)

de/sa = 5/1

mi = √(5² + 1²) = √(25 + 1) = √26

cos(2x) = sa/mi = 1/√26