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if triangle lmn has an obtuse angle at vertex m. which statements could…

Question

if triangle lmn has an obtuse angle at vertex m. which statements could be true? choose three correct answers. the angle at vertex n is acute. triangle lmn is an obtuse triangle. triangle lmn is a right triangle. the angle at vertex n is right. the angle at vertex l is right. the angle at vertex l is acute.

Explanation:

Step1: Recall triangle angle sum property

The sum of angles in a triangle is \(180^{\circ}\). An obtuse angle is greater than \(90^{\circ}\) and less than \(180^{\circ}\).

Step2: Analyze each statement

  • The angle at vertex \(N\) is acute:

Since \(\angle M>90^{\circ}\), and \(\angle L+\angle M+\angle N = 180^{\circ}\), then \(\angle L+\angle N=180^{\circ}-\angle M<90^{\circ}\). So both \(\angle L\) and \(\angle N\) must be acute. This statement can be true.

  • Triangle \(LMN\) is an obtuse triangle:

By definition, a triangle with one obtuse angle is an obtuse triangle. Since \(\angle M\) is obtuse, \(\triangle LMN\) is an obtuse triangle. This statement is true.

  • Triangle \(LMN\) is a right triangle:

A right - triangle has one right angle (\(90^{\circ}\)). If \(\angle M>90^{\circ}\), then \(\angle L+\angle N<90^{\circ}\), so there cannot be a right angle. This statement is false.

  • The angle at vertex \(N\) is right:

If \(\angle N = 90^{\circ}\), and \(\angle M>90^{\circ}\), then \(\angle L+\angle M+\angle N>180^{\circ}\), which violates the triangle angle sum property. This statement is false.

  • The angle at vertex \(L\) is right:

If \(\angle L = 90^{\circ}\), and \(\angle M>90^{\circ}\), then \(\angle L+\angle M+\angle N>180^{\circ}\), which violates the triangle angle sum property. This statement is false.

  • The angle at vertex \(L\) is acute:

Since \(\angle M>90^{\circ}\), and \(\angle L+\angle M+\angle N = 180^{\circ}\), then \(\angle L+\angle N=180^{\circ}-\angle M<90^{\circ}\). So both \(\angle L\) and \(\angle N\) must be acute. This statement can be true.

Answer:

  • The angle at vertex \(N\) is acute.
  • Triangle \(LMN\) is an obtuse triangle.
  • The angle at vertex \(L\) is acute.