What is the integral of # cos(theta)^2#? Calculus Introduction to Integration Integrals of Trigonometric Functions 1 Answer Euan S. Aug 13, 2016 #=1/2[phi + 1/2sin2phi] + C# Explanation: Use double angle formula #cos2phi = 2cos^2phi - 1# #therefore cos^2phi = 1/2(1+cos2phi)# #int cos^2phi dphi = 1/2 int (1+cos2phi) dphi# #=1/2[phi + 1/2sin2phi] + C# Answer link Related questions How do I evaluate the indefinite integral #intsin^3(x)*cos^2(x)dx# ? How do I evaluate the indefinite integral #intsin^6(x)*cos^3(x)dx# ? How do I evaluate the indefinite integral #intcos^5(x)dx# ? How do I evaluate the indefinite integral #intsin^2(2t)dt# ? How do I evaluate the indefinite integral #int(1+cos(x))^2dx# ? How do I evaluate the indefinite integral #intsec^2(x)*tan(x)dx# ? How do I evaluate the indefinite integral #intcot^5(x)*sin^4(x)dx# ? How do I evaluate the indefinite integral #inttan^2(x)dx# ? How do I evaluate the indefinite integral #int(tan^2(x)+tan^4(x))^2dx# ? How do I evaluate the indefinite integral #intx*sin(x)*tan(x)dx# ? See all questions in Integrals of Trigonometric Functions Impact of this question 7916 views around the world You can reuse this answer Creative Commons License