Đáp án+Giải thích các bước giải:

`sinalpha( 1 + cos2alpha )`

`= sinalpha( 1 + cos^2alpha - sin^2alpha )`

`= sinalpha . 2cos^2alpha`

`= sin2alpha . cosalpha`

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`-2/( tan2alpha )`

`= -2/(( 2tanalpha)/(1 - tan^2alpha ))`

`= ( -2( 1 - tan^2alpha ))/( 2tanalpha )`

`= ( tan^2alpha - 1 )/( tanalpha )`

`= tanalpha - 1/( tanalpha )`

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`2/( tanalpha - 1 ) + ( cotalpha + 1 )/( cotalpha - 1 )`

`= ( 2cotalpha - 2 + ( tanalpha - 1 )( cotalpha + 1 ))/(( tanalpha - 1 )( cotalpha - 1 ))`

`= ( 2cotalpha - 2 + 1 - cotalpha + tanalpha - 1 )/( 1 - cotalpha - tanalpha + 1 )`

`= ( cotalpha + tanalpha - 2 )/( 2 - cotalpha - tanalpha )`

`= -1`