Courses
Courses for Kids
Free study material
Offline Centres
More
Store Icon
Store
seo-qna
SearchIcon
banner

Find the integral of cos4x dx?

Answer
VerifiedVerified
441.9k+ views
like imagedislike image
Hint: As per the given question we have to find the integral of cos4x which is quite easy to evaluate using various identities of cos function and then integrating it. Firstly, we will simplify it to the power of one and then integrate it in order to get the answer in simple steps with less chances of errors.

Complete step by step answer:
In the given question we need to find the integral of the cosine function raised to power four which is cos4x and also we will make use of the fact that the integration of cosx is sinx and 1dx is x.
Now, in order to integrate the given cosine function what we need to do is use the cosine identity as follows:
cos2x=1+cos2x2
So, now we need to integrate cos4xdx and applying the identity we get,
 I=(1+cos2x2)2dx14(1+cos22x+2cos2x)dx
Now, applying the identity again and integrating using the fact that integration of cosx is sinx and 1dx is x we get,
14(1+cos22x+2cos2x)dx14(x+sin2x+(1+cos4x2)dx)14(x+sin2x+12x+sin4x8)
Now, simplifying it further we get,
14(sin2x+32x+sin4x8)
Therefore, the integral of the given cosine function cos4xdx we get 14(sin2x+32x+sin4x8).

Note: We can also do the given question using a reduction formula and attain the answer but in this we may get the complex step and attain the wrong answer. Also, what we need to do is not to get confused in the integration and differentiation of cos and sine functions.