Integration by Parts Formula
Integration by parts uses the formula ∫u dv = uv - ∫v du, which comes from rearranging the product rule for derivatives. This technique is especially useful when you have a product of functions and direct integration seems impossible.
When choosing which function to call "u," remember the helpful acronym "LIATE" which stands for Logarithmic, Inverse trigonometric, Algebraic (polynomials), Trigonometric, and Exponential functions. Functions earlier in this list make better choices for "u."
For example, to solve ∫(sin 5x)dx, we set u = 3x+1 and dv = sin 5x dx. After finding du = 3dx and v = -⅕cos 5x, we substitute into our formula: uv - ∫v du. This gives us -⅕(cos 5x) + ⅗∫cos 5x dx, which simplifies to -⅕(cos 5x) + ⅗(⅕sin 5x) + c.
💡 Pro Tip: When choosing which function to be "u" and which to be "dv," pick the function for "u" that simplifies when differentiated, and the function for "dv" that remains manageable when integrated.



