a) sina = 21/29
sin^2a + cos^2a = 1
(21/29)^2 + cos^2a = 1
cos^2a = 1 - 441/841
cos^2a = 400/841
cosa = 20/29
tga = sina/cosa = 21/29 * 29/20 = 21/20
ctga = 1/tga = 20/21
b) cosa = 1/5
sin^2a + cos^2a = 1
sin^2a = 1 - cos^2
sin^2a = 1 - 1/25
sin^2a = 24/25
sina= √6/5
tga = sina/cosa = √6/5 * 1/5 = √6
ctga = 1/tga = √6/6
c) sina = √3/2
sin^2a + cos^2a = 1
(√3/2)^2 + cos^2a = 1
cos^2a = 1 - 3/4
cos^2a = 1/4
cosa = 1/2
tga = sina/cosa = √3/2 * 2 = √3
ctga = 1/tga = √3/3
