dễ quá x(13/19+7/19-1/19)=230 X x 19/19=230 X x 1=230 X=230:1 X=230 chi tiết đó nha :>

`Answer:`

\(S_4=\frac{3}{5}+\frac{3}{5^2}+\frac{3}{5^3}+...+\frac{3}{5^{99}}\)

\(\Rightarrow S_4=3.\left(\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{99}}\right)\)

\(\Rightarrow\frac{S_4}{3}=\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{99}}\)

\(\Rightarrow5.\frac{S_4}{3}=5.\left(\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{99}}\right)\)

\(\Rightarrow\frac{5}{3}.S^4=1+\frac{1}{5}+\frac{1}{5^2}+\frac{1}{5^3}+...+\frac{1}{5^{98}}\)

\(\Rightarrow\frac{5}{3}.S_4-\frac{S_4}{3}=\left(1+\frac{1}{5}+...+\frac{1}{5^{98}}\right)-\left(\frac{1}{5}+\frac{1}{5^2}+...+\frac{5}{5^{99}}\right)\)

\(\Rightarrow\frac{4}{3}.S_4=1+\frac{1}{5}+...+\frac{1}{5^{98}}-\frac{1}{5}-\frac{1}{5^2}-...-\frac{1}{5^{99}}\)

\(\Rightarrow\frac{4}{3}.S_4=1+\left(\frac{1}{5}-\frac{1}{5}\right)+...+\left(\frac{1}{5^{98}}-\frac{1}{5^{98}}\right)-\frac{1}{5^{99}}\)

\(\Rightarrow\frac{4}{3}.S_4=1-\frac{1}{5^{99}}\)

\(\Rightarrow\frac{4}{3}.S_4=\frac{5^{99}-1}{5^{99}}\)

\(\Rightarrow S_4=\frac{\left(5^{99}-1\right).3}{4.5^{99}}\)

X x 13/19 + X x 7/19 - X x 1/19 = 230

X x (13/19 + 7/19 - 1/19) = 230

X x 1 = 230

X = 230

haizzzz...

chịu

\(P=45a+20b+\dfrac{27}{b^2}+\dfrac{108}{a}\)

\(P=27\left(a+\dfrac{4}{a}\right)+\left(b+b+\dfrac{27}{b^2}\right)+18\left(a+b\right)\)

\(P\ge27.2\sqrt{\dfrac{4a}{a}}+3\sqrt[3]{\dfrac{27b^2}{b^2}}+18.5=207\)

Dấu "=" xảy ra khi \(\left(a;b\right)=\left(2;3\right)\)

\(45a+20b+\frac{27\left(a+4b^2\right)}{ab^2}=45a+20b+\frac{27}{b^2}+\frac{108}{a}\)

\(=\left(\frac{108}{a}+27a\right)+\left(\frac{27}{b^2}+b+b\right)+18\left(a+b\right)\)

\(\ge108+9+18\cdot5=207\)

(Hôm nay bn t i c k mik đủ r thì thôi, mai t i c k trả mik sau)

a) \(\frac{5}{3}+\frac{4}{3}=\frac{9}{3}=3\)

b) \(\frac{2}{3}-\frac{3}{8}=\frac{16}{24}-\frac{9}{24}=\frac{7}{24}\)

c) \(\frac{6}{5}\times3=\frac{18}{5}\)

d) \(\frac{3}{7}\div\frac{3}{4}=\frac{3}{7}\times\frac{4}{3}=\frac{4}{7}\)

Bài 1: Tính 

a) 5/3 + 4/3 = 9/3

 b) 2/3 - 3/8 = 7/24

 c) 6/5 x 3 = 6/5 x 3/1 = 18/15

 d) 3/7 : 3/4 = 12/21

K nha

thời gi@n để đi đến tỉnh = 54 : 45 = 1,2 h = 1h 12 phút

ng đó dên tỉnh lúc = 6 h 30 phút + 1h 12 phút = 7 h 42 phút