Hey everyone. So up to this point, we've spent a lot of time dealing with the sine and cosine functions, discussing their graphs and different ways that the graphs can be transformed, such as being stretched or shifted in some way. Well, in this video, we're going to learn that we can graph more trigonometric functions such as the secant and cosecant. This might sound a bit scary at first, but don't worry because it turns out we can actually use the graphs that we learned about for sine and cosine to graph the cosecant and secant. So, without further ado, let's get right into this.
Now recall that the cosecant and secant are reciprocals. They're reciprocal identities for the sine and cosine. Cosecant is ⅛ divided by the sine and secant is ⅛ divided by the cosine. You can use these relationships to figure out what their graphs look like. So I'm just going to jump right into the cosecant graph.
If I go ahead and take the reciprocal for all these outputs that I see, the reciprocal of ⅛ is just ⅛. The reciprocal of negative ⅛ is negative ⅛ because one divided by negative ⅛ would be negative ⅛, and then the reciprocal of ⅛ is just ⅛ there. So, that means at an x value of π/2, we'll have ⅛. For 3π/2, we're going to have negative ⅛, and then for 5π/2, we're going to have ⅛ again. Now I'm also going to need to take the reciprocal of these values.
But notice that all of these values are zero. And if I take the reciprocal of zero, that's just going to be ⅛ divided by zero. But this is actually a problem, because recall that in math, it's a fundamental rule that we cannot divide by zero. So what does this mean? Well, that means that every place we see zero for our sine value, our cosecant is going to be undefined.
So all of these values will be undefined. And for undefined values, what we're basically saying in this instance is that they're approaching infinity, and infinity is not a number, so we can't define it. So what we can do is we can take asymptotes, and we can draw them where we see the sine function reach zero. So we're going to have an asymptote at an x value of zero. We'll have another asymptote at an x value of π.
And we'll have another asymptote at an x value of 2π. Now from here, I need to figure out how the rest of the graph is going to behave. And the way that I can do this is by simply observing how the sine function behaves. Notice how the sine function gets smaller and smaller as we go to the left and as we go to the right. And what happens if you take the reciprocal of a number that gets smaller and smaller?
Well, the whole fraction is going to get bigger and bigger. And because of this, our cosecant function is going to increase as we go to the left and as we go to the right. So we, in essence, end up with this kind of smiley face thing happening right here. And it turns out that this logic stays true for all the other points. So at this point right here, we can see that our value is actually getting bigger and bigger as we go to the left and right.
If the values are getting bigger, that means that the reciprocal is going to get smaller and smaller. And likewise, we can see right here that these values get smaller here, so it's going to get bigger and bigger as you blow up to the left and to the right at this point. So notice how we end up with these smiley and frowny faces where we have the peaks and valleys respectively. Now let's also take a look and see how the secant function behaves. Well, I can use the same logic by taking the reciprocal of all these values for the cosine.
So the reciprocal of ⅛ is ⅛, and then we have the reciprocal of negative ⅛ and the reciprocal of ⅛. So going to our graph, our points are going to be at ⅛ at the peak there, at negative ⅛ for the valley at x value of π, and then at another peak, we're going to have ⅛ as well. Now because secant is a reciprocal of the cosine, all the places that we see zero for the cosine are going to be undefined for the secant. So when doing this, we can actually draw asymptotes at all these undefined values. So at x value of π/2, we're going to have an asymptote.
At 3π/2, we're going to have another asymptote. And then at 5π/2, we're going to have another asymptote. Now just like we saw with the cosecant, this graph is a reciprocal of the cosine. So just like with the cosecant graph, we're going to see these kind of smiley faces and frowny faces where the peaks and valleys are. So notice how these two graphs end up looking very similar.
The really key difference between these two graphs is where the asymptotes are located. Because notice, for the cosecant, we ended up with asymptotes at zero, π, 2π, basically just integer multiples of π. And for the secant, we ended up with asymptotes at π/2, 3π/2, 5π/2, or basically just odd multiples of π/2. Now something that's really nice about the cosecant and secant graphs is it turns out that you can use all the same transformation rules that you use for the sine and cosine. So, all the stretches and shifts for the cosecant and secant function that we learned about are going to hold true.
And to see this, let's actually take a look at an example. So in this example, we are asked to graph the function y is equal to the cosecant of 2x. Now you may be a little bit curious wh