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Ta có: \(\dfrac{1}{5}+\dfrac{4}{10}+\dfrac{9}{15}+\dfrac{16}{20}+\dfrac{25}{25}+\dfrac{36}{30}+\dfrac{49}{35}+\dfrac{64}{40}+\dfrac{81}{45}\)
\(=\dfrac{1}{5}+\dfrac{2}{5}+\dfrac{3}{5}+\dfrac{4}{5}+\dfrac{5}{5}+\dfrac{6}{5}+\dfrac{7}{5}+\dfrac{8}{5}+\dfrac{9}{5}\)
\(=\dfrac{45}{5}=9\)
bỏ tạm 38/25 ra
=(9/10-11/15) +(13/21-15/28) +(197/4851-199/4950)
=1/6+1/12+1/20+...+1/49*50=2450
=3-2/2x3+4-3/3x4+5-4/4x5+....50-49/49x50
=1/2-1/3+1/3-...-1/50
1/2-1/50=12/25
=38/25+12/25=50/25
=2
= (8x15x24x35x...x99) / (9x16x25x36x...x100)
= (4x2x5x3x6x2x2x5x7x...x9x11) / (9x4x2x2x5x5x6x3x2x...x25x4)
= 11/(4x25)
= 11/100
Mình không chắc lắm
1/5 + 4/10 +9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45
=1/5 + 2/5 + 3/5 +...+ 9/5
=45/5=9
\(\frac{1}{5}+\frac{4}{10}+\frac{9}{15}+\frac{16}{20}+\frac{25}{25}+\frac{36}{30}+\frac{49}{35}+\frac{64}{40}+\frac{81}{45}\)
\(=\frac{1}{5}+\frac{1}{5}+\frac{3}{5}+\frac{4}{5}+\frac{5}{5}+\frac{6}{5}+\frac{7}{5}+\frac{8}{5}+\frac{9}{5}\)
\(=\frac{\left(9+1\right)\cdot9:2}{5}=\frac{45}{5}=9\)
\(\frac{9}{15}\times\frac{25}{36}=\frac{9\times25}{15\times36}=\frac{1\times5}{3\times4}=\frac{5}{12}\)
\(\frac{8}{27}\times9=\frac{8\times9}{27}=\frac{8\times1}{3}=\frac{8}{3}\)
1/5+4/10+9/15+25/25+36/30+49/35+64/40+81/45
=1/5 + (4/10:2) + (9/15:3)+25/25 + (36/30:6)+ (49/35:7) + (64/40:8) + (81/45:9)
=1/5 + 1/5 + 1/5 + 1 + 1/5 + 1/5 + 1/5 + 1/5
=1/5 x 7 + 1
=12/5
