Special Triangles in GeometryA series of free High School Geometry Video Lessons from Brightstorm.
45 45 90 Triangles A 45 45 90 triangle is a special type of isosceles right triangle where the two legs are congruent to one another and the non-right angles are both equal to 45 degrees. Many times, we can use the Pythagorean theorem to find the missing legs or hypotenuse of 45 45 90 triangles. The ratio of the sides to the hypotenuse is always 1:1:square root of two.
30 60 90 Triangles A 30 60 90 triangle is a special type of right triangle. What is special about 30 60 90 triangles is that the sides of the 30 60 90 triangle always have the same ratio. Therefore, if we are given one side we are able to easily find the other sides using the ratio of 1:2:square root of three. This special type of right triangle is similar to the 45 45 90 triangle.
Arc Length Commonly confused with arc measure, arc length is the distance between the endpoints along the circle. Arc measure is a degree measurement, equal to the central angle that forms the intercepted arc. Arc length is a fraction of the circumference of the circle and calculated that way: find the circumference of the circle and multiply by the measure of the arc divided by 360.
Secants A secant is a line, ray, or line segment that intersects a circle in two places. Three points are covered: (1) secants that intersect in a circle which divide each other proportionally, (2) the angle formed by secants which intersects in a circle and is half the sum of the intercepted arcs, and (3) two secants drawn from the same point outside a circle that form an angle whose measure is half the difference of the intercepted arcs.
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