In isosceles triangle ABC, the degree measure of angle ABC is 30°, wha

Solution

Given:
• In isosceles triangle ABD, the degree measure of angle ABC is 40°

To find:
• The difference between the maximum possible degree measure of the largest angle in the triangle ABC and the minimum possible degree measure of the largest angle in the triangle ABC

Approach and Working:
As there is no details provided about the angle ABC except the value, we can have 2 possible cases.

Case 1:
If angle ABC is one of the same angle in the base, then the 3 angles of triangle ABC are 40°, 40°, and 100°

• Largest angle = 100°

Case 2:
If angle ABC is the vertex angle, then the 3 angles of triangle ABC are 40°, 70°, and 70°

• Largest angle = 70°

Therefore the difference between the maximum largest angle and minimum largest angle = maximum possible largest angle – minimum possible largest angle = 100° - 70° = 30°

Hence, the correct answer is option C.

Answer: C

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