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Giải
a : Vì 0.2=0.1
0.3=0.2+0.1
0.4=0.3+0.1
............1.9=1.8+0.1
Vậy dãy số trên có khoang cách đều là 0.1 đơn vị
Số lượng số hạng là
{1.9-0.1} : 0.1 + 1 = 19 số
tổng dãy số là
{1.9+0.1} x 19 : 2 = 19
b ta có a/4 + a/3 = 21.35
a x 1/4 + a x 1/3 = 21.35
a x { 1/4+1/3} = 21.35
a x 7/12 = 21.35
a = 21.35 : 7/12
a = 36.6
d/s a 19
b 36.6
a) \(\frac{\left(1,9-0,1\right):0,1+1}{2}\times\left(0,1+1,9\right)\))
Còn lại bạn tự tính nha!Nếu muốn pt công thức thì nói luôn nha!
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Sửa đề:1/1*3+2/3*7+3/7*13+4/13*21+5/21*31
=1/2(2/1*3+4/3*7+6/7*13+8/13*21+10/21*31)
=1/2(1-1/3+1/3-1/7+...+1/21-1/31)
=1/2*30/31=15/31
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\(\frac{2.3.\left(1+2.3+7.7\right)}{3.5.\left(1+2.3+7.7\right)}=\frac{2}{5}\)
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a, 21.35-3.25.7=21.35-21.25=21.(35-25)=21.10=210
b, 77-11.(30+7)=77-330-77=-330
c, 85.(35-27)-35.(85-27)=85.35-85.27-35.85+35.27=0
d, 47.(45-15)-47.(45+15)=47.45-47.15-47.45-47.15=-2(47.15)=1410
a, 21.35-3.25.7=21.35-21.25=21.10=210
b,77-11.(30+7)=77-11.30-11.7=-11.30=-330
c,85.(35-27)-35.(85-27)=85.35-85.27-85.35+35.27=27.(-50)=-1350
d, 47.(45-15)-47.(45+15)=47.45-47.15-47.45-47.15=-47.30=-1410
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Giải:
a) \(\dfrac{5^3.90.4^3}{25^2.3^2.2^{13}}\)
\(=\dfrac{5^3.5.3^2.2.\left(2^2\right)^3}{\left(5^2\right)^2.3^2.2^{13}}\)
\(=\dfrac{5^4.3^2.2.2^6}{5^4.3^2.2^{13}}\)
\(=\dfrac{5^4.3^2.2^7}{5^4.3^2.2^{13}}\)
\(=\dfrac{1}{2^6}=\dfrac{1}{64}\)
b) \(\dfrac{15^2.16^4-15^3.16^3}{12^2.20^3-20^2.12^3}\)
\(=\dfrac{15^2.16^3.16-15^2.16^3.15}{12^2.20^2.20-20^2.12^2.12}\)
\(=\dfrac{15^2.16^3.\left(16-15\right)}{12^2.20^2.\left(20-12\right)}\)
\(=\dfrac{\left(3.5\right)^2.\left(2^4\right)^3.1}{\left(3.2^2\right)^2.\left(2^2.5\right)^2.8}\)
\(=\dfrac{3^2.5^2.2^{12}}{3^2.\left(2^2\right)^2.\left(2^2\right)^2.5^2.2^3}\)
\(=\dfrac{3^2.5^2.2^{12}}{3^2.5^2.2^4.2^4.2^3}\)
\(=\dfrac{3^2.5^2.2^{12}}{3^2.5^2.2^{11}}\)
\(=2\)
c) \(\dfrac{2.3+4.6+14.21}{3.5+6.10+21.35}\)
\(=\dfrac{2.3+2.3.2.2+2.3.7.7}{3.5+3.5.2.2+3.5.7.7}\)
\(=\dfrac{2.3+2.3.4+2.3.49}{3.5+3.5.4+3.5.49}\)
\(=\dfrac{2.3.\left(1+4+49\right)}{3.5.\left(1+4+49\right)}\)
\(=\dfrac{2.3}{3.5}\)
\(=\dfrac{2}{5}\)
Chúc bạn học tốt!
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\(\frac{3}{5.11}+\frac{5}{11.21}+\frac{7}{21.35}+\frac{9}{35.53}=\frac{1}{2}\left(\frac{1}{5}-\frac{1}{11}+\frac{1}{11}-\frac{1}{21}+\frac{1}{21}-\frac{1}{35}+\frac{1}{35}-\frac{1}{53}\right)=\frac{1}{2}\left(\frac{1}{5}-\frac{1}{53}\right)=\frac{1}{10}-\frac{1}{106}
a=36,6
a:4+a:3=21.35
<=>a:4+a:3=735
<=>a:(4+3)=735
<=>a:7=735
=>a=735x7
=>a=5145