This figure is an acute triangle.

He taught me how to calculate the area of an obtuse triangle.

His company was a short-lived regime.

I am attending cooking classes to learn the technique of filleting fish.

When learning Japanese grammar, understanding the tri-grade conjugation is important.

He can do a perfect handstand.

They are always together like the Three Musketeers at school.

His trilogy is very popular.

I cannot know the thoughts buried deep inside her heart.

I can't understand what's in his mind.