```
# sind(x) and cosd(x) are accurate for x which are multiples
# of 90 and 180 degrees, while tand(x) is problematic.
x <- seq(0, 720, by = 90)
sind(x) # 0 1 0 -1 0 1 0 -1 0
cosd(x) # 1 0 -1 0 1 0 -1 0 1
tand(x) # 0 Inf 0 -Inf 0 Inf 0 -Inf 0
cotd(x) # Inf 0 -Inf 0 Inf 0 -Inf 0 Inf
x <- seq(5, 85, by = 20)
asind(sind(x)) # 5 25 45 65 85
asecd(sec(x))
tand(x) # 0.08748866 0.46630766 1.00000000 ...
atan2d(1, 1) # 45
```

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