He was diagnosed with mental illness.

There are times when we perform calculations with the haversine in trigonometry.

He is a pessimist, always looking at the bad side of the world.

This regular tetrahedron is composed of equilateral triangles on all sides.

He made a model of a regular tetrahedron.

My father works at a paper mill.

My father has been working as a silk manufacturer for many years.

I attend psychotherapy sessions every week.

My father works at a paper mill.

He achieved success as a silk manufacturer.