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\(\frac{1}{5}+\frac{4}{10}+...+\frac{81}{45}=\frac{1}{5}+\frac{2}{5}+\frac{3}{5}+...+\frac{9}{5}=\frac{1+2+3+...+9}{5}=\frac{45}{5}=9\)
1/5 + 4/10 + 9/15 + 16/20 + 25/25 + 36/30 + 49/35 + 64/40 + 81/45
=1/5 + 2/5 + 3/5 + 4/5 + 5/5 + 6/5 + 7/5 + 8/5 + 9/5
=45/5 = 9
a) \(\frac{16.17-5}{16.16+11}=\frac{16.16+16-5}{16.16+11}=\frac{16.16+11}{16.16+11}=1\)1
b ) \(\frac{5}{30}+\frac{15}{90}+\frac{25}{150}+\frac{35}{210}+\frac{45}{270}=\frac{1}{6}+\frac{1}{6}+\frac{1}{6}+\frac{1}{6}+\frac{1}{6}\)
\(=\frac{1}{6}.5=\frac{5}{6}\)
a) (16x17-5)/(16x16+11)=(16x16-5+16)/(16x16+11)=1
b) (1x5)/(6x5)+(3x5)/(18x5)+...+(9x5)/(54x5)
=1/6+1/6+1/6+1/6+1/6
=5/6
1/10+4/20+9/30+16/40+25/50+36/60+49/70+64/80+81/90
=1/10+2/10+3/10+4/10+5/10+6/10+7/10+8/10+9/10
=1+2+3+4+5+6+7+8+9/10
=45/10 (tự rút gọn)
Bạn giúp người khác mà muốn trả công à.
Bạn chỉ cần rút gọn các PS về MS bằng 5 rồi tính bình thường.
1/2+1/6+1/12+...+1/110
=1/1.2+1/2.3+1/3.4+...+1/10.11
=1-1/2+1/2-1/3+1/3-1/4+...+1/10-1/11
=1-1/11=10/11
b ) \(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}=\left(\frac{1}{2}-\frac{1}{3}\right)+\left(\frac{1}{3}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{5}\right)+\left(\frac{1}{5}-\frac{1}{6}\right)+\left(\frac{1}{6}-\frac{1}{7}\right)=\frac{1}{2}-\frac{1}{7}=\frac{5}{14}\)
215 - 15 x { 25 - 15 : [ 3 x 45 - 3 x ( 50 - 2 x 3 ) ] }
= 215 - 15 x { 25 - 15 : [ 3 x 45 - 3 x 44 ] }
= 215 - 15 x { 25 - 15 : 3 }
= 215 - 15 x 20
= 215 - 300
= -85
b) \(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\)
\(=\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}\)
\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)
\(=\frac{1}{2}-\frac{1}{7}=\frac{5}{14}\)
=(1-1/2)+(1-1/6)+(1-1/12)+.......+(1-1/90)
= 9 - (1/2 +5/6 +1/12+.......+1/90)
= 9- (1-1/2 + 1/2 - 1/3+1/3 -1/4 +....... +1/9-1/10)
=9-(1-1/10)
=9-9/10=81/10
=(1-1/2)+(1-1/6)+(1-1/12)+.......+(1-1/90)
= 9 - (1/2 +5/6 +1/12+.......+1/90)
= 9- (1-1/2 + 1/2 - 1/3+1/3 -1/4 +....... +1/9-1/10)
=9-(1-1/10)
=9-9/10=81/10
\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}=\frac{9}{10}\)
Bạn biết bài này rồi phải không =.="
a) 5/30+15/90+25/150+35/210+45/270
=1/6+1/6+1/6+1/6+1/6
=1/6 x 5
=5/6
b) 1/2+1/6+1/12+1/20+....+1/56
=1/1x2+1/2x3+1/3x4+1/4x5+.....1/7x8
=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+.......-1/7+1/7-1/8
=1/1-1/8
=7/8
c) mình chịu
thank you bn nhìu nha