Question

use a counter - example to show that the following conjecture is false. △abc is a right triangle, so ∠a measures 90°. choose the correct answer below.

Explanation:

Step1: Analyze the statement

The statement claims that in right - triangle $\triangle ABC$, $\angle A$ measures $90^{\circ}$. But in a right - triangle, any of the three angles can be the right angle.

Step2: Examine the options

We need to find a right - triangle where $\angle A$ is not the right angle. Option C shows a right - triangle $\triangle ABC$ where the right angle is at $\angle A$, so it doesn't disprove the statement. Option B shows a right - triangle with the right angle at $\angle B$. Option A is an acute - triangle. Option D is a non - right triangle. The right - triangle in option B is a counter - example as it is a right - triangle but $\angle A
eq90^{\circ}$.

Answer:

B