By giving a counterexample,show that the following statement is not true.
$p:$ If all the angles of a triangle are equal,then the triangle is an obtuse-angled triangle.

(N/A) The given statement is of the form 'if $q$ then $r$'.
$q:$ All the angles of a triangle are equal.
$r:$ The triangle is an obtuse-angled triangle.
The statement $p$ is false if we can find a case where $q$ is true but $r$ is false.
In an equilateral triangle,all three angles are equal to $60^{\circ}$.
Since $60^{\circ} < 90^{\circ}$,an equilateral triangle is an acute-angled triangle,not an obtuse-angled triangle.
Thus,the statement $p$ is false because we have found a counterexample (the equilateral triangle) where the premise is true but the conclusion is false.