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D = \(\dfrac{1}{7^2}\) - \(\dfrac{2}{7^3}\) + \(\dfrac{3}{7^4}\) - \(\dfrac{4}{7^5}\) +........+ \(\dfrac{201}{7^{202}}\) - \(\dfrac{202}{7^{203}}\)
7 \(\times\) D = \(\dfrac{1}{7}\) - \(\dfrac{2}{7^2}\) + \(\dfrac{3}{7^3}\) - \(\dfrac{4}{7^4}\) + \(\dfrac{5}{7^5}\) -.......- \(\dfrac{202}{7^{202}}\)
7D +D = \(\dfrac{1}{7}\) - \(\dfrac{1}{7^2}\) + \(\dfrac{1}{7^3}\) - \(\dfrac{1}{7^4}\) + \(\dfrac{1}{7^5}\) -.........-\(\dfrac{1}{7^{202}}\) - \(\dfrac{202}{7^{203}}\)
D = ( \(\dfrac{1}{7}\) - \(\dfrac{1}{7^2}\) + \(\dfrac{1}{7^3}\) - \(\dfrac{1}{7^4}\) + \(\dfrac{1}{7^5}\) -.........-\(\dfrac{1}{7^{202}}\) - \(\dfrac{202}{7^{203}}\)) : 8
Đặt B = \(\dfrac{1}{7}\) - \(\dfrac{1}{7^2}\) + \(\dfrac{1}{7^3}\) - \(\dfrac{1}{7^4}\) + \(\dfrac{1}{7^5}\) -........+\(\dfrac{1}{7^{201}}\).-\(\dfrac{1}{7^{202}}\)
7 \(\times\) B = 1 - \(\dfrac{1}{7}\)+\(\dfrac{1}{7^2}\) - \(\dfrac{1}{7^3}\) + \(\dfrac{1}{7^4}\) - \(\dfrac{1}{7^5}\) +.........- \(\dfrac{1}{7^{201}}\)
7B + B = 1 - \(\dfrac{1}{7^{202}}\)
B = ( 1 - \(\dfrac{1}{7^{202}}\)) : 8
D = [ ( 1 - \(\dfrac{1}{7^{202}}\)): 8 - \(\dfrac{202}{7^{203}}\)] : 8
D = \(\dfrac{1}{64}\) - \(\dfrac{1}{64.7^{202}}\) - \(\dfrac{202}{7^{203}.8}\) < \(\dfrac{1}{64}\)
=1+(2-3-4+5)+3-4-5+6)+...+(200-201-202+203)+204
=1+0+0+...+0+204
=1+204
=205
tinh
1+2 -3 -4 +5+3-4-5+6 +4-5-6 +7 + ....+200-201 -202 + 203 + 204 =1+0+...+0+204=1+204=205.
bn k cho mik nha. ^-^ thanks bn trc.
Tính nhanh:
a) 1-2-3+4+5-6-7+8+9-10-.......+200+201-202-203
Đặt \(A=\text{1-2-3+4+5-6-7+8+9-10-.......+200+201-202-203}\)
\(A=1+\left(2-3-4+5\right)+\left(6-7-8=9\right)+\left(10-11-12+13\right)+... \)\(+\left(298-299-300+301\right)+302\)
\(A=1+0+0+0+...+0+302\)
\(A=1+302\)
\(A=303\)
Phần B làm sau nha!
Tính :
1-2+3-4+5-6+...+201-202
=(1-2)+(3-4)+(5-6)+...+(201-202) (có 101 cặp)
=(-1)+(-1)+(-1)+...+(-1)
=(-1).101=-101.
Tìm x là số nguyên :
30-(x+1)=-17
x+1=30-(-17)
x+1=47
x=47-1
x=46
Vậy x=46.
x(|15|-10)=53
x(15-10)=53
x.5=53
x=53:5
x=52=25
Vậy x=25
2x+5=7-x-5
2x+x+5=7-5
3x+5=2
3x=2-5
3x=-3
x=(-3):3
x=-1
Vậy x=-1.
a) \(\dfrac{13}{20}+\dfrac{3}{5}+x=\dfrac{5}{6}\)
\(\Rightarrow\dfrac{5}{4}+x=\dfrac{5}{6}\)
\(\Rightarrow x=\dfrac{5}{6}-\dfrac{5}{4}\)
\(\Rightarrow x=\dfrac{-5}{12}\)
b) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\dfrac{-1}{3}\)
\(\Rightarrow x+\dfrac{1}{3}=\dfrac{11}{15}\)
\(\Rightarrow x=\dfrac{11}{15}-\dfrac{1}{3}\)
\(\Rightarrow x=\dfrac{2}{5}\)
c)\(\dfrac{-5}{8}-x=\dfrac{-3}{20}-\dfrac{-1}{6}\)
\(\dfrac{-5}{8}-x=\dfrac{1}{60}\)
\(\Rightarrow x=\dfrac{-5}{8}-\dfrac{1}{60}\)
\(\Rightarrow x=\dfrac{-77}{120}\)
d) \(\dfrac{3}{5}-x=\dfrac{1}{4}+\dfrac{7}{10}\)
\(\Rightarrow\dfrac{3}{5}-x=\dfrac{19}{20}\)
\(\Rightarrow x=\dfrac{3}{5}-\dfrac{19}{20}\)
\(\Rightarrow x=\dfrac{-7}{20}\)
e) \(\dfrac{-3}{7}-x=\dfrac{4}{5}+\dfrac{-2}{3}\)
\(\Rightarrow\dfrac{-3}{7}-x=\dfrac{2}{15}\)
\(\Rightarrow x=\dfrac{-3}{7}-\dfrac{2}{15}\)
\(\Rightarrow x=\dfrac{-59}{105}\)
g) \(\dfrac{-5}{6}-x=\dfrac{7}{12}+\dfrac{-1}{3}\)
\(\Rightarrow\dfrac{-5}{6}-x=\dfrac{1}{4}\)
\(\Rightarrow x=\dfrac{-5}{6}-\dfrac{1}{4}\)
\(\Rightarrow x=\dfrac{-13}{12}\)
a) Ta có:
\(2^{300}=2^{3\cdot100}=\left(2^3\right)^{100}=8^{100}\)
\(3^{200}=3^{2\cdot100}=\left(3^2\right)^{100}=9^{100}\)
Mà: \(8< 9\)
\(\Rightarrow8^{100}< 9^{100}\)
\(\Rightarrow2^{300}< 3^{200}\)
b) Ta có:
\(3^{500}=3^{5\cdot100}=\left(3^5\right)^{100}=243^{100}\)
\(7^{300}=7^{3\cdot100}=\left(7^3\right)^{100}=343^{100}\)
Mà: \(243< 343\)
\(\Rightarrow243^{100}< 343^{100}\)
\(\Rightarrow3^{500}< 7^{300}\)
c) Ta có:
\(8^5=\left(2^3\right)^5=2^{3\cdot5}=2^{15}=2\cdot2^{15}\)
\(3\cdot4^7=3\cdot\left(2^2\right)^7=3\cdot2^{2\cdot7}=3\cdot2^{14}\)
Mà: \(2< 3\)
\(\Rightarrow2\cdot2^{14}< 3\cdot2^{14}\)
\(\Rightarrow8^5< 3\cdot4^7\)
d) Ta có:
\(202^{303}=202^{3\cdot101}=\left(202^3\right)^{101}=8242408^{101}\)
\(303^{202}=303^{2\cdot101}=\left(303^2\right)^{101}=91809^{101}\)
Mà: \(8242408>91809\)
\(\Rightarrow8242408^{101}>91809^{101}\)
\(\Rightarrow202^{303}>303^{202}\)
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Bằng 5^57/7,71 cách giải 12:0,1+7/^1-729=5^57/7,71
5^57/7,71-3:3x2+2:4=5^57/7,71
Chúc bạn học giỏi nhe :)))) 👍👍👍👍👍👍👍👍👍