Question

if triangle rst is an acute triangle, then ( mangle s ) must be
less than ( 90^{circ} ).
equal to ( 90^{circ} ).
equal to ( 100^{circ} ).
greater than ( 90^{circ} ) and less than ( 180^{circ} ).

Explanation:

An acute triangle is defined as a triangle where all three interior angles are acute angles. An acute angle is an angle whose measure is less than \(90^\circ\). So, in an acute triangle \(RST\), each angle (including \(\angle S\)) must be less than \(90^\circ\). An angle equal to \(90^\circ\) is a right angle (right triangle), an angle equal to \(100^\circ\) or greater than \(90^\circ\) and less than \(180^\circ\) is an obtuse angle (obtuse triangle), which does not fit the definition of an acute triangle.

Answer:

A. less than \(90^\circ\)