Tính giá trị biểu thức sau:
1.\(B=\left(1-\dfrac{1}{2}\right)\left(1-\dfrac{1}{3}\right)......\left(1-\dfrac{1}{n+1}\right)\)với n thuộc N
2.\(A=\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}\)
3.\(C=-66.\left(\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{11}\right)+124.\left(-37\right)+63.\left(-124\right)\)
4.\(D=\dfrac{7}{4}\left(\dfrac{33}{12}\dfrac{3333}{2020}\dfrac{333333}{303030}\dfrac{33333333}{42424242}\right)\)
giúp mik nhé