Đáp án:
ta có 1/2^2 +1/3^2 +1/4^2 +...+1/50^2 < 1/(1*2) + 1/(2*3) + 1/(3*4) + ..+ 1/(49*50)
mà
1/(1*2) + 1/(2*3) + 1/(3*4) + ..+ 1/(49*50)= 1-1/2 +1/2 -1/3 +...-1/50 = 1-1/50
suy ra 1/2^2 +1/3^2 +1/4^2 +...+1/50^2 < 1-1/50
hay 1/2^2 +1/3^2 +1/4^2 +...+1/50^2 < 1