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2010-02-19T14:35:35+01:00
Sin²α+cos²α=1
sin²α=1-cos²α
sin²α=1-4/25
sin²α=21/25
sinα=√21/5

tgα=sinα/cosα=√21/2

ctgα=cosα/sinα=2/√21
2010-02-19T14:38:03+01:00
A²+b²=c²
a²+2²=5²
a²=21
a=√21

sinα=a/c
sinα=√21/5

cosα=2/5

tgα=a/b
tgα=√21/2

ctgα=b/a
ctgα=2/√21 /* √21/√21
ctgα=2√21/21