Interior angles of a right angled triangle in pythagorus theorem.

Answer 1

Using math!
Given any 2 sides, you can use Pythagoras' theorem to find the 3rd one.
Or if you have 1 angle, 1 side, use trigonometry.

|\
a | \ c
| \
|___\
b
Of the above right angled triangle let A,B,C be the angles opposite to a,b,c respectively and C=90°
c^2=a^2+b^2
sin(A)=a/c
sin(B)=b/c
sin(C)=1
cos(A)=b/c
cos(B)=a/c
cos(C)=0
tan(A)=a/b
tan(B)=b/a
tan(C)=undefined

Trigonometrical functions are found in the math module

Answer 2

Why stop at right triangles? You can use the law of cosines to find the interior angles of any triangle: c^2 = a^2 + b^2 - 2*a*b*Cos(angle c). Move terms around and use the arcCosine function.

Answer 3

Addendum to Pagasus' answer. The mnemonic many of us learn (from the perspective of any angle "theta") is:

SOH CAH TOA (Sounds like: Soak-a-toe-a)

Sine(theta) = Opposite / Hypotenuse
Cosine(theta) = Adjacent / Hypotenuse
Tangent(theta) = Opposite / Adjacent (or... sin/cos, which is why the right angle is undefined when cos(90) produces DIV/0)

The "arc" functions invert sine/cosine/tangent and return angles (in radians) from these ratios (e.g., math.asin() in Python).

Note that all flat triangles have inner angles that sum to 180 degrees (this means the two angles you discover should sum to 90).

Answer 4

I suppose noting this seems to be a component of an earlier question (with more parts) may help:
https://www.sololearn.com/Discuss/856644/?ref=app