use latex d d t ( 2 t e t t + 1 ) = ( 2 e t + 2 t e t ) ( t + 1 ) − 2 t e t ( t + 1 ) 2 = 2 e t ( t + 1 ) 2 − 2 t e t ( t + 1 ) 2 {\displaystyle {\frac {d}{dt}}({\frac {2te^{t}}{t+1}})={\frac {(2e^{t}+2te^{t})(t+1)-2te^{t}}{(t+1)^{2}}}={\frac {2e^{t}(t+1)^{2}-2te^{t}}{(t+1)^{2}}}} 【Aperture__的个人空间-哔哩哔哩】 https://b23.tv/cgJ7AoW
