| Pýþagórasar-samsemdir | c o s 2 𝜃 + s i n 2 𝜃 = 1 1 + t a n 2 𝜃 = s e c 2 𝜃 1 + c o t 2 𝜃 = c s c 2 𝜃 cos 2 θ + sin 2 θ = 1 1 + tan 2 θ = sec 2 θ 1 + cot 2 θ = csc 2 θ |
| Samsemdir jafnstæðra og oddstæðra falla | c o s ( − 𝜃 ) = c o s 𝜃 s e c ( − 𝜃 ) = s e c 𝜃 s i n ( − 𝜃 ) = − s i n 𝜃 t a n ( − 𝜃 ) = − t a n 𝜃 c s c ( − 𝜃 ) = − c s c 𝜃 c o t ( − 𝜃 ) = − c o t 𝜃 cos (− θ ) = cos θ sec (− θ ) = sec θ sin (− θ ) = − sin θ tan (− θ ) = − tan θ csc (− θ ) = − csc θ cot (− θ ) = − cot θ |
| Fyllihornasamsemdir | |
| Grunnsamsemdir | |
| Samlagningar- og frádráttarsamsemdir | |
| Tvöföldunarformúlur | s i n ( 2 𝜃 ) = 2 s i n 𝜃 c o s 𝜃 c o s ( 2 𝜃 ) = c o s 2 𝜃 − s i n 2 𝜃 c o s ( 2 𝜃 ) = 1 − 2 s i n 2 𝜃 c o s ( 2 𝜃 ) = 2 c o s 2 𝜃 − 1 t a n ( 2 𝜃 ) = 2 t a n 𝜃 1 − t a n 2 𝜃 sin ( 2 θ ) = 2 sin θ cos θ cos ( 2 θ ) = cos 2 θ − sin 2 θ cos ( 2 θ ) = 1 − 2 sin 2 θ cos ( 2 θ ) = 2 cos 2 θ − 1 tan ( 2 θ ) = 2 tan θ/1 − tan 2 θ |
| Helmingunarformúlur | |
| Lækkunarformúlur | |
| Margfeldi í summu | |
| Summa í margfeldi | |
| Sínusreglan | |
| Kósínusreglan | 𝑎 2 = 𝑏 2 + 𝑐 2 − 2 𝑏 𝑐 c o s 𝛼 𝑏 2 = 𝑎 2 + 𝑐 2 − 2 𝑎 𝑐 c o s 𝛽 𝑐 2 = 𝑎 2 + 𝑏 2 − 2 𝑎 𝑏 c o s 𝛾 a 2 = b 2 + c 2 − 2 b c cos α b 2 = a 2 + c 2 − 2 a c cos β c 2 = a 2 + b 2 − 2 a b cos γ |
