1. Tinh:
\(P=\left(1-\dfrac{1}{3}\right)\left(1-\dfrac{1}{6}\right)\left(1-\dfrac{1}{10}\right)\left(1-\dfrac{1}{15}\right)...\left(1-\dfrac{1}{780}\right)\)
2. Tim \(a,b\in N\) de co: \(\dfrac{a}{3}-\dfrac{2}{b}=\dfrac{1}{3}\)
Bai tuy hoi kho nhung mong moi nguoi giup do...
Đọc tiếp
1. Tinh:
\(P=\left(1-\dfrac{1}{3}\right)\left(1-\dfrac{1}{6}\right)\left(1-\dfrac{1}{10}\right)\left(1-\dfrac{1}{15}\right)...\left(1-\dfrac{1}{780}\right)\)
2. Tim \(a,b\in N\) de co: \(\dfrac{a}{3}-\dfrac{2}{b}=\dfrac{1}{3}\)
Bai tuy hoi kho nhung mong moi nguoi giup do nhe!
2.
\(\dfrac{a}{3}-\dfrac{2}{b}=\dfrac{1}{3}\)
\(\dfrac{a\times b-3\times2}{3\times b}\)\(=\dfrac{1}{3}\)
\(\dfrac{a\times b-6}{3\times b}=\dfrac{1}{3}\)
\(\Rightarrow3\times\left(a\times b-6\right)=1\times\left(3\times b\right)\)
\(3ab-18=3b\)
\(3ab-18-3b=0\)
\(3ab-3b=18\)
\(3b\left(a-1\right)=18\)
Mà \(18=1.18=2.9=3.6\)
\(\Rightarrow3b\left(a-1\right)=1.18=2.9=3.6\)
còn lại bạn tự làm các trường hợp ra nhé,mk lười lắm