If $u=\mathrm{g}\left( x \right)$ is a differentiable function whose range is an interval $I$ and $\mathrm{f}$ is continuous on $I$ , then
$\int{\mathrm{f}\left[ \mathrm{g}\left( x \right) \right]}\mathrm{ g}'\left( x \right)\mathrm{ d}x=\int{\mathrm{f}\left( u \right)}\mathrm{ d}u$.
This method of integration is sometimes known as reverse chain rule or change of variables. 
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We do not require any formulae memorisation using this method other than the standard integrals learnt in secondary school or in the formulae sheet (MF26). This method is acceptable in H2 A Level Examinations, and it is mathematically grounded. 
The -substitution method replaces all standard forms that is required for students to memorise, e.g.,
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If $u=\mathrm{g}\left( x \right)$ is a differentiable function whose range is an interval $I$ and $\mathrm{f}$ is continuous on $I$ , then

$\displaystyle\displaystyle \int{\mathrm{f}\left[ \mathrm{g}\left( x \right) \right]}\mathrm{ g}'\left( x \right)\mathrm{ d}x=\displaystyle\displaystyle \int{\mathrm{f}\left( u \right)}\mathrm{ d}u$.

This method of integration is sometimes known as **reverse chain rule** or **change of variables**. 

We do not require any formulae memorisation using this method other than the standard integrals learnt in secondary school or in the formulae sheet (MF26). This method is **acceptable in H2 A Level Examinations**, and it is **mathematically grounded**.  

The  -substitution method replaces all standard forms that is required for students to memorise, e.g.,

Method of Substitution (Cancelling Method)

Method of Substitution (Cancelling Method)

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