 In the videos that you watched yesterday, you worked with sine, cosine, and tangent when you were given all of the side measures. What we're going to do today is we are going to be given the side measures and we are going to try to find out what the angle measures are. So we are going to use this idea of inverse. So before we talk about trigonometry, let's just think about real quick what is the inverse of these operations. Hopefully you can fill in the inverses of each of these. So inverse of addition, we would know is subtraction. Inverse of subtraction would be addition. Inverse of multiplication would be division. If I can write the division sign there, that's kind of messy. And the inverse of division would be multiplication. And then the inverse of x squared, we would use the square root. So when solving equations like 3x equals negative 27, we use the inverse of multiplication to find x. Because we know this is 3 times x, so the opposite or the inverse operation is divide 3. So if we divide both sides by 3, we get our answer x equals negative 9. In trigonometry, we can find the measure of the angle by using the inverse of sine, cosine, or tangent. And what you will notice if you take a quick look at your calculator, if you look above the sine, cosine, and tangent buttons, you're going to see sine with a little negative 1, cosine with a little negative 1, and tangent with a little negative 1. And those are the inverse sine, inverse cosine, and inverse tangent buttons that you'll be using.