He went to the station to say goodbye to her.

His explanation was very easy to understand.

He is good at understanding new concepts quickly.

After listening to his story, my understanding of the mood deepened.

He drew a triangle on the blackboard.

Please calculate the area of this right-angled triangle.

He was drawing a tridecagon shape.

This figure is an acute triangle.

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

I will test whether you understand this problem or not.