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a)\(19\frac{5}{8}:\frac{7}{12}-15\frac{1}{4}:\frac{7}{12}\)
=(\(19\frac{5}{8}-15\frac{1}{4}\)):\(\frac{7}{12}\)
=(\(19\frac{10}{16}-15\frac{4}{16}\)):\(\frac{7}{12}\)
=\(4\frac{6}{16}:\frac{7}{12}\)
=\(\frac{35}{8}:\frac{7}{12}\)
=\(\frac{35}{8}\cdot\frac{12}{7}\)
=\(\frac{15}{2}\)
b)2/5*1/3-2/15:1/5+3/5*1/3
=2/15-2/3+1/5
=-8/15+1/5
=-1/3
aidi qua dong tinh nho h chom minh nhe
S=5+5^2+5^3+5^4+...5^99
=> 5S=5^2+5^3+5^4+...5^100
=> 5S-S=4S=(5^2+5^3+5^4+...5^100)-(5+5^2+5^3+5^4+...5^99)
=> 4S = 5100-5
=> S=(5100-5)/4
S=5*5^2*5^3*5^4*...5^99
=> S=51+2+3+...+99
=> S=5((99+1).99):2
=> S=54950
(3x-2)+16=125+12
(3x-2)+16=137
3x-2=121
3x=123
x=41
5s=5^2+5^3+5^4+5^5+......+5^100
5s-s=5^100-5
4s=5^100-5
s=(5^100-5):4
kick nhé
\(\left(3x-2\right)^2+4^2=5^3+3.2^2\\ \Rightarrow\left(3x-2\right)^2+16=125+12\\ \Rightarrow\left(3x-2\right)^2=121\\ \Rightarrow3x-2=11\\ \Rightarrow x=\frac{13}{3}\)
S= \(5+5^2+5^3+.....+5^{99}\\ \Rightarrow5S=5^2+5^3+5^4+.....+5^{100}\\ \Rightarrow4S=5^{100}-5\\ \Rightarrow\frac{5^{100}-5}{4}\)
S=\(5.5^2.5^3.5^4.........5^{99}=5^{1+2+3+4+....+99}=5^{4950}\)
S=5+52+53+54+...+599
5S=52+53+54+...+599
5S-S=(52-52)+(53-53)+...+(599-599)+5100+5
S=(5100+5):4
(\(\dfrac{2}{3}\) - \(\dfrac{11}{7}\) + \(\dfrac{13}{5}\)) - (5 - \(\dfrac{4}{7}\) + \(\dfrac{6}{5}\)) - (\(\dfrac{11}{3}\) - \(\dfrac{3}{5}\))
= \(\dfrac{2}{3}\) - \(\dfrac{11}{7}\) + \(\dfrac{13}{5}\) - 5 + \(\dfrac{4}{7}\) - \(\dfrac{6}{5}\) - \(\dfrac{11}{3}\) + \(\dfrac{3}{5}\)
= (\(\dfrac{2}{3}\) - \(\dfrac{11}{3}\)) - (\(\dfrac{11}{7}\) - \(\dfrac{4}{7}\)) + (\(\dfrac{13}{5}\) - \(\dfrac{6}{5}\)+ \(\dfrac{3}{5}\))
= \(\dfrac{-9}{3}\) - \(\dfrac{7}{7}\) + (\(\dfrac{7}{5}\) + \(\dfrac{3}{5}\)) - 5
= - 3 - 1 + 2 - 5
= - (3 + 1) - ( 5 - 2)
= - 4 - 3
= - 7
Answer:
Bài 1:
\(\left(135-35\right).\left(-37\right)+37.\left(-42-58\right)\)
\(=100.\left(-37\right)+37.\left(-100\right)\)
\(=\left(-3700\right)+\left(-3700\right)\)
\(=-7400\)
\(-65.\left(87-17\right)-87.\left(17-65\right)\)
\(=\left(-65\right).87-\left(-65\right).17-87.17+87.65\)
\(=-\left(-65\right).17-87.17\)
\(=17.\left(65-87\right)\)
\(=-374\)
\([3.\left(-2\right)-\left(-8\right)].\left(-7\right)-\left(-2\right).\left(-5\right)\)
\(=[\left(-6\right)+8].\left(-7\right)-\left(-2\right).\left(-5\right)\)
\(=2.\left(-7\right)-10\)
\(=-24\)
Bài 2:
\(\left(-55\right).\left(-25\right).\left(-8\right)\)
\(=\left(-55\right).[\left(-25\right).\left(-8\right)]\)
\(=\left(-55\right).200\)
\(=-11000\)
\(\left(-1\right).\left(-2\right).\left(-3\right).\left(-4\right).\left(-5\right).10\)
\(=[\left(-1\right).10].[\left(-2\right).\left(-5\right)].[\left(-3\right).\left(-4\right)]\)
\(=\left(-10\right).10.12\)
\(=-1200\)
?
S= 2/3.5 + 2/5.7 +.....+ 2/37.39
= 1/3 - 1/5 + 1/5 - 1/7 + ...... + 1/37 - 1/39
= 1/3 - 1/39 =12/39