Question

Tính nhanh

B=3^2/1.3+3^2/3.5+3^2/5.7+...+3^2/95.97+3^2/97.99

Answer 1

=3.(3/1.3+3/3.5+3/5.7+...+3/95.97+3/97.99)

=3(1-1/3+1/3-1/5+1/5-1/7+...+1/95-1/97+1/97-1/99)

=3[(1-1/99)+(1/5-1/5)+(1/7-1/7)+...+(1/97-1/97)]

=3(1-1/99)=3(99/99-1/99)=3.98/99=1.98/33=98/33

Answer 2

Neu la 3 ma ko phai la 3^2 thi sao : Tinh gium minh nha .