How would you go about integrating a function which has an exponential and a cos/sin term?

For this type of integral you would need to use integration by parts twice. Remember this is where the integral of u*(dv/dx)=uv-(integral with respect to x)(v*(du/dx)). For example let's say you need to integrate sin(x)e^x, it doesn't matter which you choose to be u and dv/dx as sin(x) is cyclic and e^x doesn;t change under differnetiation/integration. And so arbitarily say u=sin(x) and dv/dx=e^x therefore du/dx=cos(x) and v=e^x. We will call the original integral I and so now we have I=sin(x)e^x-(integral with respect to x)(cos(x)e^x). then perform it again but with different variables. Now we change u=cos(x) and dv/dx=e^x, it can be usefull to use subscripts to not confuse u and v from what they previously were, therefore du/dx=-sin(x), v=e^x. From this we have I=sin(x)e^x-cos(x)e^x-(integral with respect to x)(sin(x)e^x)+c, and the integral left now is the same as the original and so equals I, hence this can be reaaranged to 2I=sin(x)e^x-cos(x)e^x+c. This can be cleaned up to get I=((sin(x)-cos(x))e^x)/2+c, is this all clear?

LR
Answered by Luke R. Maths tutor

3504 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

Express cos2x in the form a*cos^2(x) + b and hence show that the integral of cos^2(x) between 0 and pi/2 is equal to pi/a.


Find the derivative with respect to x and the x-coordinate of the stationary point of: y=(4x^2+1)^5


Find the turning points of the curve y=2x^3 - 3x^2 - 14.


Integrate 2x/(x^2+3) using the substitution u=x^2+3


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences