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Corners & Lines

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Corners & Lines

Complementary & Supplementary Angles

Complementary and supplementary angles are special pairs of angles 👯‍♀️.

Complementary angles are two angles that combine to form a corner.
Supplementary angles are two angles that combine to form a straight line.

Complementary & Supplementary Angles Calculator

Are the two angles complementary or supplementary?
No sweat! We can help you figure it out 🦸🏽‍♀️. How many of the two angles do you know?

Step 1. Determine the total angle measure.

Step 2. Find the value of the unknown angle.

If we know the measure of one of the two angles, we can use it to find the value of the missing angle.
What is the value of your given angle?
So, the value of the missing angle is .

Key Steps 🗝 How to Find Complementary & Supplementary Angles

Show steps for angles that are:

Step 1. Determine the total angle measure.

If the two angles are complementary or form a corner (right angle), then the total angle measure is .

Step 2. Find the value of the unknown angle.

If we know the measure of one of the two angles, we can use it to find the value of the missing angle.

Step 1. Determine the total angle measure.

If the two angles are supplementary or form a straight line, then the total angle measure is .

Step 2. Find the value of the unknown angle.

If we know the measure of one of the two angles, we can use it to find the value of the missing angle.
Walk through example problems and practice finding complementary and supplementary angles!

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Complementary and Supplementary Angles

Complementary and supplementary angles problems come in a few different forms. Sometimes, you'll be given a diagram with one given angle and one unknown angle:
In this case, the little box 🔲 in the corner tells us the two angles are complementary and add up to .
And if you see two angles on a straight line like this:
You'll know that the two angles are supplementary and add up to .
Other times, you might not have a diagram at all. You might be asked

What is the angle complementary to ?

In this case, the angle that is complementary to is the angle we can add to make it . So our answer is .
We might even get a wordier problem like this:

Angles A and B are supplementary. If Angle A is , what is Angle B?

This is still the same type of problem 😮. We know supplementary angles add up to , so we're looking for the angle that combines with to give us . So our answer is .
Now let's get started with some example problems!
Let's start by finding the unknown angle below:
No sweat! We can help you figure it out 🦸🏽‍♀️. How many of the two angles do you know?

Step 1. Determine the total angle measure.

If the two angles are complementary or form a corner (right angle), then the total angle measure is .

Step 2. Find the value of the unknown angle.

If we know the measure of one of the two angles, we can use it to find the value of the missing angle.
So, the value of the missing angle is .
Nice work! Let's try one more: find the unknown angle below:
No sweat! We can help you figure it out 🦸🏽‍♀️. How many of the two angles do you know?

Step 1. Determine the total angle measure.

If the two angles are supplementary or form a straight line, then the total angle measure is .

Step 2. Find the value of the unknown angle.

If we know the measure of one of the two angles, we can use it to find the value of the missing angle.
So, the value of the missing angle is .
Incredible work! If you’d like additional practice with complementary and supplementary angles, take a moment to complete the quick practice below before closing out this lesson! ⚡

Practice: Complementary & Supplementary Angles

Question 1 of 10: Find the unknown angle:

Step 1. Determine the total angle measure.

What is the total angle measure?

Step 2. Find the value of the unknown angle.

Great work! The unknown angle is  .

When you feel like you've mastered this lesson, click for a celebration ⬇️!
Incredible job, look at you go! Thanks for checking out this lesson ☺️🙏. Where to next?