Could someone help me with this question?

Test Preparation AP Test Preparation
1

<p>The diameter of a circle is one side of a triangle, and the third vertex is on the circle. What kind of triangle is formed?
A. Isosceles
B. Right
C. Acute
D. Scalene
E. Equilateral</p>

<p>The answer sheet says it is B. Right, but I don't understand. Couldn't it be scalene?</p>

2

<p>That is Thales’ theorem. Here is a visual representation:</p>

<p><a href=“http://upload.wikimedia.org/wikipedia/commons/b/bf/Animated_illustration_of_thales_theorem.gif[/url]”>http://upload.wikimedia.org/wikipedia/commons/b/bf/Animated_illustration_of_thales_theorem.gif&lt;/a&gt;&lt;/p&gt;

<p>You can read about it here: </p>

<p><a href=“http://en.wikipedia.org/wiki/Thales’_theorem[/url]”>http://en.wikipedia.org/wiki/Thales’_theorem&lt;/a&gt;&lt;/p&gt;

3

<p>The diameter is the longest chord in a circle, so then draw the other point on the circle and then connect it to the vertices of the diameter. Since the diameter creates a semi-circle, an inscribed angle in a semi-circle is always a right angle. This makes sense, because it is opposite the hypotenuse (the longest possible side which is the diameter). The triangle could be scalene, but it doesn’t have to be. However, the triangle will always be a right triangle. Tip: contradict everything until you are certain something is proven true. Hope that helps you understand it.</p>

4

<p>What class is this for?</p>

5

<p>Thank you and sorry for saying it so late! This is just a question from ACT practice test.</p>