Frage 10

A learner is asked for the base angles of an isosceles triangle with an apex angle of 40 degrees and two equal base angles. The learner writes: 180 minus 40 is 140, so each base angle is 140 degrees. Which statement names the mistake in this working and gives the correct size?

Nothing is wrong, and each base angle really is 140 degrees.
The 140 degrees covers both base angles, so each one is 70 degrees.Richtige Antwort
All three angles here are equal, so each base angle is 60 degrees.
The apex should have been subtracted from 360, so each base angle is 160 degrees.

Erklärung

Taking the apex away from the triangle total leaves 140 degrees for the two base angles combined, and since those two are equal each takes half of it, giving 70 degrees. Treating 140 degrees as a single base angle would push the three angles well past the 180 degrees a triangle has to spend.

Erklärung

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