4t-6=2(2t-3)
4t²-9=(2t+3)(2t-3)
最简公分母是2(2t+3)(2t-3)
所以3t/(4t-6)=3t(2t+3)/2(2t+3)(2t-3)
(t+1)/(4t²-9)=2(t+1)/2(2t+3)(2t-3)