why the ending symbol dx is also changed into a function of d theta and then multiplied by the integral after substitution?
27812
Understanding the differential $dx$ when doing $u$-substitution
15947
Validity of Substitutions in Integrals
118586
Confused About Trigonometric Substitution
110113
Definite and Indefinite integral give different results for piecewise function
112551
Demystify integration of $\int \frac{1}{x} \mathrm dx$
146353
Is there a way to rewrite integrals in Mathematica using u substitution?
79561
Transform to polar the following integral $\int_0^6\int_0^y x \, dx \, dy$
59617
Calculus Question - change order of integration
101550
How to change coordinates of a differential operator?
31102
Why does $\frac{1}{r}\frac{dr}{d\theta} = \cot \psi$?
46378
Trig substitution; why can we ignore the absolute value?
24545
A doubt regarding change of variables in Double Integrals.
156485
How to evaluate $\int_{0}^{2\pi}e^{\cos \theta}\cos( \sin \theta) d\theta$?
138355
Improper rational/trig integral comes out to $\pi/e$
35274
What is wrong with this substitution?
40310
How to integrate $\frac{1}{\sqrt{1+x^2}}$ using substitution?
142365
Use of substitution into the integral $\int_0^2 \frac{\arctan x}{x^2+2x+2}dx$