Question

Tính S = [ 1 + (1+2) + (1+2+3) +...+ (1+2+3+...+98) ] / (1*2 + 2*3 + 3*4 +...+ 98*99)

Answer 1

\(S=\frac{1+\left(1+2\right)+\left(1+2+3\right)+...+\left(1+2+3+...+98\right)}{1.2+2.3+3.4+....+98.99}\)

\(=\frac{1+\frac{2.3}{2}+\frac{3.4}{2}+....+\frac{98.99}{2}}{1.2+2.3+3.4+....+98.99}\)

\(=\frac{\frac{1}{2}\left(1.2+2.3+3.4+....+98.99\right)}{1.2+2.3+3.4+....+98.99}\)

\(=\frac{1}{2}\)

Answer 2

sao toàn thấy frac, left và right ko vậy?