The mathematician sketched an acute-angled triangle on the board to illustrate properties of altitudes.

The geometer carefully measured the acute angles to verify the triangle's properties.

She measured the acute angle formed by the intersecting lines before labeling the diagram.

The teacher asked the students to classify each triangle on the worksheet and to identify any acute-angled triangle.

In the competition, students were asked to classify acute-angled triangles by their side lengths and angles.