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5. (30 + 56 ) và 30 . 5 + 56.5
5 . ( 30 + 56 )
= 5.30 + 5.56
=> 5.( 30 + 56 ) = 30.5 + 56 . 5
Các câu kia cứ làm tương tự!
^^ Học tốt!
2.B=1+5+5^2+...+5^98
B=1+5^2+5^3+...+5^96+5^97+5^98
B=(1+5+5^2)+(5^3+5^4+5^5)+...+(5^96+5^97+5^98)
B=(1+5+25)+5^3.(1+5+25)+...+5^96.(1+5+25)
B=31+5^3.31`+...+5^96.31
B=(1+5^3+...+5^98).31.Suy ra B chia hết cho 31.
1. không chia hết
2. chia hết
3.
a.3^16 lớn hơn
b.3^100 lớn hơn
c.2^10+3^20+4^30 lớn hơn
d.2^30 lớn hơn
e.1991^10 lớn hơn
f.16 ^12 lớn hơn
g.(1/32)^7 lớn hơn
h.3^39 lớn hơn
Bài 1:
a; \(\dfrac{5}{18}\) + \(\dfrac{8}{19}\) - \(\dfrac{7}{21}\) + (- \(\dfrac{10}{36}\) + \(\dfrac{11}{19}\) + \(\dfrac{1}{3}\)) - \(\dfrac{5}{8}\)
= \(\dfrac{5}{18}\) + \(\dfrac{8}{19}\) - \(\dfrac{1}{3}\) -\(\dfrac{10}{36}\) + \(\dfrac{11}{19}\) + \(\dfrac{1}{3}\) - \(\dfrac{5}{8}\)
= (\(\dfrac{5}{18}\) - \(\dfrac{10}{36}\)) + (\(\dfrac{8}{19}\) + \(\dfrac{11}{19}\)) - (\(\dfrac{1}{3}\) - \(\dfrac{1}{3}\)) - \(\dfrac{5}{8}\)
= (\(\dfrac{5}{18}\) - \(\dfrac{5}{18}\)) + \(\dfrac{19}{19}\) - 0 - \(\dfrac{5}{8}\)
= 0 + 1 - \(\dfrac{5}{8}\)
= \(\dfrac{3}{8}\)
b; \(\dfrac{1}{13}\) + (\(\dfrac{-5}{18}\) - \(\dfrac{1}{13}\) + \(\dfrac{12}{17}\)) - (\(\dfrac{12}{17}\) - \(\dfrac{5}{18}\) + \(\dfrac{7}{5}\))
= \(\dfrac{1}{13}\) - \(\dfrac{5}{18}\) - \(\dfrac{1}{13}\) + \(\dfrac{12}{17}\) - \(\dfrac{12}{17}\) + \(\dfrac{5}{18}\) - \(\dfrac{7}{5}\)
= (\(\dfrac{1}{13}\) - \(\dfrac{1}{13}\)) + (\(\dfrac{12}{17}\) - \(\dfrac{12}{17}\)) + (-\(\dfrac{5}{18}\) + \(\dfrac{5}{18}\)) - \(\dfrac{7}{5}\)
= 0 + 0 + 0 - \(\dfrac{7}{5}\)
= - \(\dfrac{7}{5}\)
Bài 1 c;
\(\dfrac{15}{14}\) - (\(\dfrac{17}{23}\) - \(\dfrac{80}{87}\) + \(\dfrac{5}{4}\)) + (\(\dfrac{17}{23}\) - \(\dfrac{15}{14}\) + \(\dfrac{1}{4}\))
= \(\dfrac{15}{14}\) - \(\dfrac{17}{23}\) + \(\dfrac{80}{87}\) - \(\dfrac{5}{4}\) + \(\dfrac{17}{23}\) - \(\dfrac{15}{14}\) + \(\dfrac{1}{4}\)
= (\(\dfrac{15}{14}-\dfrac{15}{14}\)) + (\(-\dfrac{17}{23}+\dfrac{17}{23}\)) - (\(\dfrac{5}{4}\) - \(\dfrac{1}{4}\)) + \(\dfrac{80}{87}\)
= 0 + 0 - 1 + \(\dfrac{80}{87}\)
= - \(\dfrac{7}{87}\)
Ta có:
\(25^9=\left(5^2\right)^9=5^{18}\)
Vì: \(5^{17}< 5^{18}\) nên \(5^{17}< 25^9\)
Ta có:
\(3^{90}=\left(3^3\right)^{30}=27^{30}\)
\(4^{60}=\left(4^2\right)^{30}=16^{30}\)
Vì: \(27^{30}>16^{30}\) nên \(3^{90}>4^{60}\)
Bài 1:
c: \(18\cdot\left[\left(3^4\cdot29+3^4\cdot6+3^4\cdot34\right)-71\cdot1^{56}\right]-80\)
\(=18\cdot\left[3^4\left(29+6+34\right)-71\right]-80\)
\(=18\cdot\left[81\cdot69-71\right]-80\)
\(=18\cdot5518-80=99244\)
b: \(\left[19+\left(3^5-62\right)\right]\cdot x=10^3\cdot10\)
=>\(\left(243-62+19\right)\cdot x=10000\)
=>\(200x=10000\)
=>x=10000:200=50
Bài 2:
\(25^9=\left(5^2\right)^9=5^{18}>5^{17}\)
\(3^{90}=\left(3^3\right)^{30}=27^{30};4^{60}=\left(4^2\right)^{30}=16^{30}\)
mà 27>16
nên \(3^{90}>4^{60}\)