 Hi, I'm welcome to the session. I am Deepika and I'm going to help you to solve the following question. The question says evaluate integral of cos 4x into cos 3x dx So let's start the solution. Let I is equal to given integral which is integral of cos 4x cos 3x dx Now let us multiply and divide this integral by 2. So we have i is equal to 1 over 2 integral of 2 cos 4x cos 3x dx Now we know that cos c plus cos d is equal to 2 cos c plus d over 2 into cos c minus d over 2. So by using this formula we have i is equal to 1 over 2 integral of cos 7x plus cos x dx and this is again equal to 1 over 2 into now integral of cos 7x is sin 7x over 7 plus integral of cos x which is sin x plus c and this is again equal to sin 7x over 14 plus sin x over 2 plus c So sin 7x over 14 plus sin x over 2 plus c is the answer of the above question This completes our session. I hope the solution is clear to you and you have enjoyed the session Bye and have a nice day