In the figure, triangle BDE has the following angle measures: angle B = 40 degrees, angle D = 60 degrees, and angle E = 80 degrees.

Investigate a pattern between triangle BDE and ABC and make a conjecture about the measure of angle C.

1 answer

In triangle BDE, the angles are given as follows:

  • \( \angle B = 40^\circ \)
  • \( \angle D = 60^\circ \)
  • \( \angle E = 80^\circ \)

To verify these angles form a triangle, we check the sum of the angles: \[ \angle B + \angle D + \angle E = 40^\circ + 60^\circ + 80^\circ = 180^\circ \] This confirms that triangle BDE is valid.

Now, let's assume that there is a triangle ABC where angles \( A \) and \( B \) correspond to angles \( D \) and \( E \) in triangle BDE respectively. This means:

  • \( \angle A \) corresponds to \( \angle D = 60^\circ \)
  • \( \angle B \) corresponds to \( \angle E = 80^\circ \)

Using the property that the sum of the angles in any triangle equals \( 180^\circ \), we can find the measure of angle \( C \): \[ \angle A + \angle B + \angle C = 180^\circ \] Substituting the known angles: \[ 60^\circ + 80^\circ + \angle C = 180^\circ \] Calculating for \( \angle C \): \[ \angle C = 180^\circ - 60^\circ - 80^\circ = 40^\circ \]

With this investigation, we can make a conjecture regarding the measure of angle C: If angles in triangle ABC correspond to the angles in triangle BDE such that \( \angle A = \angle D\) and \( \angle B = \angle E\), then it follows that: \[ \angle C = \angle B \] This implies that the measure of angle C should be equal to the measure of angle B in triangle BDE, which is \( 40^\circ \).

Thus, the conjecture can be stated as: If triangle ABC corresponds to triangle BDE such that \( \angle A = \angle D \) and \( \angle B = \angle E \), then \( \angle C = \angle B \) of triangle BDE.