= 5-2/2x5+8-5/5x8+11-8/8x11+14-11/11x14
=(1/2-1/5)+(1/5-1/8)+(1/8-1/11)+(1/11-1/14)
=(1/2+1/5+1/8+1/11)-(1/5+1/8+1/11+1/14)
=1/2-1/14
=3/7
Vậy B=3/7
B = 3/2x5 + 3/5x8 + 3/8x11 + 3/11x14
B = 1/2 - 1/5 + 1/5 - 1/8 + ..... + 1/14 - 1/17
B = 1/2 - 1/17
B = 15/34
B= \(\frac{3}{2}\)- \(\frac{3}{5}\) + \(\frac{3}{5}\)- \(\frac{3}{8}\)+ \(\frac{3}{8}\)- \(\frac{3}{11}\)+ \(\frac{3}{11}\)+ \(\frac{3}{14}\)
=\(\frac{3}{2}\)- \(\frac{3}{14}\)
= \(\frac{9}{7}\)