3/7x2/11+3/7:11+3/7:11/8 giải giúp mịn kèm theo cách giải nhe
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20 - 19 + 18 - 17 + 16 - 15 + 14 - 13 + 12 - 11 + 10 - 9 + 8 - 7 + 6 - 5 + 4 - 3 + 2 - 1
= ( 20 - 19 ) + ( 18 - 17 ) + ( 16 - 15 ) + ( 14 - 13 ) + ( 12 - 11 ) + ( 10 - 9 ) + ( 8 - 7 ) + ( 6 - 5 ) + ( 4 - 3 ) + ( 2 - 1 )
= 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1
= 1 . 10
= 10
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a, 11 + 112 + 113 + ... + 117 + 118
= (11 + 112) + (113 + 114) + ... + (117 + 118)
= 11(1 + 11) + 113(1 + 11) + ... + 117(1 + 11)
= 11.12 + 113.12 + .... + 117.12
= 12(11 + 113 + ... + 117) chia hết cho 12
b, 7 + 72 + 73 + 74
= (7 + 73) + (72 + 74)
= 7(1 + 72) + 72(1 + 72)
= 7.50 + 72.50
= 50(7 + 72) chia hết cho 50
c, 3 + 32 + 33 + 34 + 35 + 36
= (3 + 32 + 33) + (34 + 35 + 36)
= 3(1 + 3 + 32) + 34(1 + 3 + 32)
= 3.13 + 34.13
= 13(3 + 34) chia hết cho 13
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\(A=\frac{4}{7\cdot9}+\frac{4}{9\cdot11}+...+\frac{4}{59\cdot61}=2\cdot\left(\frac{2}{7\cdot9}+\frac{2}{9\cdot11}+...+\frac{2}{59\cdot61}\right)\)
\(=2\cdot\left(\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{59}-\frac{1}{61}\right)=2\cdot\left[\left(\frac{1}{7}-\frac{1}{61}\right)+\left(\frac{1}{9}-\frac{1}{9}\right)+...+\left(\frac{1}{59}-\frac{1}{59}\right)\right]\)\(=2\cdot\left[\left(\frac{61}{427}-\frac{7}{427}\right)+0+...+0\right]=2\cdot\frac{54}{427}=\frac{108}{427}\)
Cách làm thì đúng rồi nhưng mk k chắc tính đúng, nhẩm thôi
xl bạn nhé nhưng bạn hiểu nhầm r ( chắc do mình ) nó là \(\frac{4\cdot9}{7}\)nhé bạn =))
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a.\(y:\dfrac{4}{5}=\dfrac{11}{8}\)
\(y=\dfrac{11}{8}\times\dfrac{4}{5}\)
\(y=\dfrac{11}{10}\)
b.\(\dfrac{11}{3}-y=\dfrac{1}{9}\)
\(y=\dfrac{11}{3}-\dfrac{1}{9}\)
\(y=\dfrac{32}{9}\)
c.\(\dfrac{1}{7}\times x=\dfrac{8}{5}\)
\(x=\dfrac{8}{5}:\dfrac{1}{7}\)
\(x=\dfrac{56}{5}\)
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\(\dfrac{-3}{7}.\dfrac{2}{11}+\left(\dfrac{-3}{7}\right).\dfrac{9}{11}+1.\left(\dfrac{-3}{7}\right)=\left(\dfrac{-3}{7}\right).\left(\dfrac{2}{11}+\dfrac{9}{11}+1\right)=\left(\dfrac{-3}{7}\right).\left(1+1\right)=\dfrac{-3}{7}.2=\dfrac{-6}{7}\)
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-3/11.(-22)/66.121/15
=(-3).(-22).121
11.66.15
=11
15
3/7.2/5.7/3.20.19/72
=3.2.7.20.19
7.5.3.72
=76
16
6/7.8/13+6/13.9/7-3/13.6/7
=6/7.8/13+6/7.9/13-3/13.6/7
=6/7.(8/13+9/13-3/13)
=6/7.14/13
=12/13
-1/4.152/11+68/4.(-1)/11
=152/4.(-1)/11+68/4.(-1)/11
=(-1)/11.(152/4+68/4)
=(-1)/11.220/4
=-110/22
-5/7.2/11+(-5)/7.9/11+12/7
=-5/7.2/11+-5/7.9/11+12/7
=-5/7.(2/11+9/11)+12/7
=-5/7.1+12/7
=(-5)/7+12/7
=7/7
=1
146/13-(18/7+68/13)
=146/13-18/7-68/13
=(146/13-68/13)-18/7
=78/13-18/7
=6-18/7
=42/7-18/7
=24/7
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Ta có : A = 1 + 3 + 32 + .....+ 320
=> 3A = 3 + 32 + 33 +.....+ 321
=> 3A - A = 321 - 1
=> 2A = 321 - 1
=> A = \(\frac{3^{21}-1}{2}\)
Nên : B - A = \(\frac{3^{21}}{2}-\frac{3^{21}-1}{2}=\frac{3^{21}-3^{21}+1}{2}=\frac{1}{2}\)
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Ta có:1-2+3-4+5-6+7-8+9-10+11
=(-1)+(-1)+(-1)+(-1)+(-1)+11
=(-5)+11
=6
Vây:1-2+3-4+4-5+5-6+7-8+9-10+11=6
ks nhé!Học tốt!:))