Needham's area is roughly in the shape of an acute, northward-pointing triangle.
From the en.wikipedia.org
Assume x is the small angle in the acute triangle and let m equal the valve of the two larger equal angles.
From the tierneylab.blogs.nytimes.com
The orthocenter lies inside the triangle if and only if the triangle is acute.
From the en.wikipedia.org
When one thinks of a triangle, likewise, it is always obtuse, right-angled or acute.
From the en.wikipedia.org
Fat triangle is obtuse and skinny triangle is acute, so x must be acute because it is in both triangles, and must be the angle opposite the equal sides in the fat triangle.
From the tierneylab.blogs.nytimes.com
As a result, the triangle in this picture is anything but acute.
From the time.com
Then for the obtuse triangle let w be the obtuse angle then x will be the two acute angles.
From the tierneylab.blogs.nytimes.com
The trigonometric functions for acute angles can be defined as ratios of the sides of a right triangle.