S 2 a b sinα

S 2 a b sinαS 2 a b sinαS 2 a b sinαS 2 a b sinα
S 2 a b sinαS 2 a b sinαS 2 a b sinαS 2 a b sinαS 2 a b sinαS 2 a b sinαS 2 a b sinαS 2 a b sinα
S 2 a b sinαS 2 a b sinαS 2 a b sinα