When one angle is right, you can’t go wrong.
Pythagorean theorem all the way:
Summed squares of short sides are the square of long,
You should be fluent in this, night and day.

But do not mix up summed squares with square roots,
For then you err as movie Scarecrow does:
Isosceles instead of right, to boot,
Or maybe math is diff’rent there, in Oz.

Lopsided triangles are too obtuse,
More compact ones an acute pain can cause:
The rules are tight, so don’t play fast and loose,
Euclidian’s not space, but still has laws.

    And when, at last, geometry you see,
    Your mind gets wrecked by trigonometry.