integrating using t formulas.. (1 Viewer)

[govich]

hi guys, just wondering, when u use the substitution t = tan(x/2), pretty much everyone memorises that dx = 2/1+t² dt..

do we have to show working in getting from t=tan(x/2) to this every time or is it ok to just write it down straight away??

same goes for the sinx, cosx etc substitutions.. can i just write cos x = (1-t²)/(1+t²) etc ?

 

[ToO LaZy ^*]

mm..i tend to work out the tan(x/2) formula but just write down the cosx/sinx formulas without working.

i think it depends on the marker, so ask your teacher just to be sure..but i'm sure it won't really matter.

 

[BlackJack]

Yes, you should be able to do that once you state t's definition:

t = tan (x/2)
cos x=... (any of the t ratios)

 

[:: ck ::]

always derive ... 3 lines only

 

[Maianbarian]

I normaly forget them so I just derive it