Triangle ABC is isosceles. If angle A measures $30°$, what is the measure of angle C?

• A. $25°$
• B. $60°$
• C. $30°$
• D. $75°$

Answer: (B)

Verified step by step guidance

1. Recall that in any triangle, the sum of the interior angles is always \(180^\circ\). This is a fundamental property of triangles.
2. Since triangle ABC is isosceles, it has at least two equal angles. Identify which angles could be equal based on the given information.
3. Given that angle A measures \(30^\circ\), consider the possibilities for the equal angles. If angle A is one of the equal angles, then the other equal angle must also be \(30^\circ\).
4. Calculate the measure of the third angle (angle C) by subtracting the sum of the two equal angles from \(180^\circ\) using the formula: \(\text{angle C} = 180^\circ - 2 \times 30^\circ\).
5. Simplify the expression to find the measure of angle C, which completes the solution.