Tan 2x = 1 - tan y / 1 + tan y , jika 2x + y = π/4

jawab
2x + y = π/4
2x= π/4 - y

tan (2x) = (1 - tan y)/(1 + tan y)
tan (π/4 -y ) = (1 - tan y)/(1 +tan y)

tan (π/4 - y) =
= (tan π/4 - tan y) /(1 + tan π/4 (tan y)
= (1 - tan y)/(1 + tan y)
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