1.tìm x
a) (\(\dfrac{2}{11.13}+\dfrac{2}{13.15}+...+\dfrac{2}{19.21}).462-[2,04:(x+1,05)]:0,12=19\)
b) \(\dfrac{1}{24.25}+\dfrac{1}{25.26}+...+\dfrac{1}{29.30}+x:\dfrac{1}{3}=-4\)
2. thực hiện phép tính
a)\(\dfrac{15}{28}-\dfrac{186}{116}-\dfrac{121}{462}+\dfrac{189}{198}\)
b)\((1+\dfrac{1}{1.3}).(1+\dfrac{1}{2.4}).(1+\dfrac{1}{3.5})...(1+\dfrac{1}{99.100})\)