Question

Plisssss tolong bangeeeet buat uts besok

Answer 1

Cos 10 / cos 50. cos 40 =
= cos 10 / { 1/2 ( 2 cos 50. cos 40)}
= 2 cos 10 / (cos 90 + co 10)
= 2 cos 10 /(0+ cos 10)
= 2  cos 10/cos 10
 = 2

tan 2x = 2

2 tan x / ( 1- tan² x) = 2
2 tan x = 2 ( 1 - tan² x)
2 tan x = 2 - 2 tan ²x

2 tan² x + 2 tan x = 2
tan² x + tan x = 1
(tan x + 1/2)²  = 1 + 1/4 = 5/4

tan x + 1/2 = √(5/4) = 1/2 √5
tan x = - 1/2 + 1/2 √5
tan x  = 1/2 ( -1 + √5)
tan x = 1/2 (√5  -  1)