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## Get ready for Algebra 2

### Course: Get ready for Algebra 2>Unit 5

Lesson 3: Ratios in right triangles

# Using right triangle ratios to approximate angle measure

Because of similarity, all right triangles with a given acute angle measure have equal ratios between their side lengths. So if we know two of the side lengths of a right triangle, we can figure out the angle measures, too! Created by Sal Khan.

## Want to join the conversation?

• Hi, I don't understand why Sal uses opposite leg length/hypotenuse length. Shouldn't it be adjacent length/ hypotenuse length? Can you help me, thx.
• He could have used it but you see we only have the value of opposite side and the hypotenuse. So in order to figure out the ratio he went on with opposite over hypotenuse
• What is the significance of the 'm' in m∠D?
• It's short for 'measure'. ∠D is the actual angle D, the geometric plane figure. m∠D is the measure of the angle, which is a number like 25º.
• what is a 'leg'? at ? THANKS
(1 vote)
• A leg of a right triangle is a side other than the hypotenuse. The triangle has one hypotenuse and two legs.

We also use the term for isosceles triangles; a leg is one of the pair of congruent sides.
• How do you know the difference between the adjacent and the opposite leg length?
I always get confused with these two names.
• It appears that you can pick out the hypotenuse (longest side opposite the 90 degree angle). Adjacent means next to (like two rooms with a door between them, you walk right in). This forms the reference angle with the hypotenuse. Opposite would be like having to walk across a hall before going in the room, so if you start at the reference angle, you have to walk through the middle of the triangle to find the opposite side.
• what is a hypotenuse or a adjacent length? thanks.
(1 vote)
• Hypotenuse is always the longest side of a right triangle across from the 90 degree angle. One of the two acute angles will be a reference angle, so adjacent side forms the reference angle with the hypotenuse. The opposite side requires you to go through the middle of the triangle from the reference angle.
• pls be sneak peek
(1 vote)
• ion even know what happening
(1 vote)
• why does it say that these are the approximate ratios for angle measures 25 degrees, 35 degrees, and 45 degrees when it doesn't even add up to 180 degrees?
(1 vote)
• That is the angle value for the sin , cos , and tan of the angle