At this point in the course, we've learned a ton of different rules for finding the integrals of various functions. And we've learned a lot of those rules based on the idea that taking an integral is really just the reverse process of taking a derivative. And now that we're faced with finding the integral of our general exponential function, \( b^x \), we're going to use that same idea here. So let's go ahead and jump right into things. Now recall that when finding the derivative of our general exponential function, again, that's \( b^x \), we multiplied \( b^x \) by the natural log of \( b \).
So when finding the derivative of something like \( 7^x \), this gives us \( 7^x \times \ln(7) \). So now when faced with finding the integral of functions like this \( 7^x \), we just need to reverse this process. So when finding the integral of any general exponential function, we are now going to be dividing \( b^x \) by the natural log of \( b \) instead of multiplying. So coming down to our rule box here, when we take the integral of \( b^x \, dx \), this is going to give us \( \frac{b^x}{\ln(b)} \). Then, of course, since this is an indefinite integral, we need to add on that constant of integration \( c \).
Now looking at this rule, we have certain restrictions on our base \( b \) that it has to be greater than zero and not equal to one, but these are just restrictions based on the definition of a general exponential function and aren't typically something you're going to have to worry about. So let's go ahead and apply this rule to our integral here when we integrate \( 7^x \, dx \). Now here, I can see that I have this base of seven. So with \( b \) equal to seven, applying my rule here, this is going to give me \( \frac{7^x}{\ln(7)} \). Then, of course, plus that constant of integration, \( c \).
And that's all there is to it. Having reversed our rule for finding the derivative to now find the integral. Now, we can use all of the rules for integrals that we've already learned along with this new rule, so let's go ahead and work through one additional example. Here we're asked to evaluate the indefinite integral of \( 3 \times \left(\frac{1}{2}\right)^x + 8^x \, dx \). Now depending on how comfortable you are with integrals at this point, you may be able to do this all in one go.
But I'm going to go ahead and break this down step by step just so you can actually see what I'm doing along the way. Now because I have two different functions being added together here, I'm going to go ahead and split this into two integrals being added together using my sum rule. So this is going to be equal to the integral of \( 3 \times \left(\frac{1}{2}\right)^x \, dx \), and then plus the integral of \( 8^x \, dx \). Now I can do one more thing here to simplify this. I can use my constant multiple rule to pull that three out front of this integral, making this three times the integral of \( \left(\frac{1}{2}\right)^x \, dx \).
So now let's go ahead and find what this integral is. Now looking at this first term here, taking that constant, I'm going to multiply three times the integral of \( \left(\frac{1}{2}\right)^x \, dx \). So here I can see that this integral has a \( b \) value equal to one half. So when applying this rule here, I'm just plugging in that one half everywhere that \( b \) is. So this is going to be equal to \( \frac{\left(\frac{1}{2}\right)^x}{\ln\left(\frac{1}{2}\right)} \).
Then adding that together with my other integral here, here I can see that I have a base of eight. So plugging eight in where \( b \) is for my rule here, this is going to give me \( \frac{8^x}{\ln(8)} \). Then because we're working with indefinite integrals here, I need to go ahead and add on that constant of integration, \( c \). Now this is already an acceptable answer, but I can rewrite certain things here slightly based on exponential and log properties, and this may be something that's expected of you. So let's go ahead and rewrite this using our exponential and log properties.
Now the thing that I see here is that I have this fraction raised to the power of \( x \) and I also have the natural log of a fraction. Now I can do some rewriting here, so \( \left(\frac{1}{2}\right)^x \). I can raise one and two in my numerator and denominator to the power of \( x \). So this gives me three times one to the power of \( x \) over two to the power of \( x \). Then when rewriting this natural log of one half, I could rewrite this as natural log of two to the power of negative one.
Then keeping all of my other terms the same here, \( 8^x \) over the natural log of eight plus that constant of integration \( c \). Now simplifying this to its most simple form, one to the \( x \) is just always going to be one. So my numerator here is just three times one, and that's just three. Then I'm going to move that two to the \( x \) to the bottom there. Then the natural log of two to the power of negative one, I can pull that negative one out front using my log property here to make this whole term negative.
So this becomes negative three over two to the power of \( x \) times the natural log of two. Then adding on my other term here, keeping it the same, \( 8^x \) over the natural log of eight plus that constant of integration \( c \). So now we've fully simplified this using our exponential and log properties, and this is our final answer. Now we're going to continue getting practice with this new rule coming up in the next couple of videos. I'll see you there.