...ko biết 

đặt 1+3+...+3^2024 là A

3A=3+3^2+...+3^2025

3A-A=(3+3^2+...+3^2025)-(1+3+...+3^2024)

2A=3^2025-1

A=3^2025-1/2

7: \(\dfrac{x}{7}=\dfrac{-6}{21}\)

=>\(\dfrac{x}{7}=\dfrac{-2}{7}\)

=>x=-2

8: \(\dfrac{x}{15}=\dfrac{3}{5}+\dfrac{-2}{3}\)

=>\(\dfrac{x}{15}=\dfrac{9}{15}-\dfrac{10}{15}=-\dfrac{1}{15}\)
=>x=-1

9: \(-\dfrac{2}{3}-\dfrac{1}{3}\left(2x-5\right)=\dfrac{3}{2}\)

=>\(-\dfrac{2}{3}-\dfrac{2}{3}x+\dfrac{5}{3}=\dfrac{3}{2}\)

=>\(-\dfrac{2}{3}x+1=\dfrac{3}{2}\)

=>\(-\dfrac{2}{3}x=\dfrac{3}{2}-1=\dfrac{1}{2}\)

=>\(x=\dfrac{-1}{2}:\dfrac{2}{3}=\dfrac{-3}{4}\)

10: \(\left(2x+\dfrac{3}{5}\right)^2-\dfrac{9}{25}=0\)

=>\(\left(2x+\dfrac{3}{5}+\dfrac{3}{5}\right)\left(2x+\dfrac{3}{5}-\dfrac{3}{5}\right)=0\)

=>\(2x\left(2x+\dfrac{6}{5}\right)=0\)

=>\(\left[{}\begin{matrix}x=0\\x=-\dfrac{6}{5}:2=-\dfrac{3}{5}\end{matrix}\right.\)

giúp mình với, mình đang cần gấp ạ

\(75\%\cdot x-2\dfrac{1}{2}=1\dfrac{2}{5}\)

=>\(x\cdot0,75=1,4+2,5=3,9\)
=>\(x=3,9:0,75=5,2\)

\(\dfrac{1}{5\cdot8}+\dfrac{1}{8\cdot11}+...+\dfrac{1}{x\left(x+3\right)}=\dfrac{7}{180}\)

=>\(\dfrac{3}{5\cdot8}+\dfrac{3}{8\cdot11}+...+\dfrac{3}{x\left(x+3\right)}=\dfrac{7}{60}\)

=>\(\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11}+...+\dfrac{1}{x}-\dfrac{1}{x+3}=\dfrac{7}{60}\)

=>\(\dfrac{1}{5}-\dfrac{1}{x+3}=\dfrac{7}{60}\)

=>\(\dfrac{1}{x+3}=\dfrac{1}{5}-\dfrac{7}{60}=\dfrac{12}{60}-\dfrac{7}{60}=\dfrac{5}{60}=\dfrac{1}{12}\)

=>x+3=12

=>x=9

cảm ơn cậu nhé

đề bài dou bạn?

tính tổng dãy số đó 

1\(\dfrac{13}{15}.\left(0,5\right)^2.3+\left(\dfrac{8}{15}-1\dfrac{19}{60}\right):1\dfrac{23}{24}\)

\(\dfrac{28}{25}.\dfrac{1}{4}.3+\left(\dfrac{8}{15}-\dfrac{79}{60}\right):\dfrac{47}{24}\)

= \(\dfrac{118}{100}.\dfrac{25}{100}.3+\left(-\dfrac{47}{60}\right):\dfrac{47}{24}\)

= \(\dfrac{177}{200}+-\dfrac{2}{5}\)

= \(\dfrac{177}{200}+-\dfrac{80}{200}=\dfrac{97}{200}\)

mẹ mua về một chai dầu .sau khi dùng 1

trọng lượng của túi hàng là:

\(P=10\cdot34=340\left(N\right)\)

Trọng lượng của An là \(P=10\cdot38=380\left(N\right)\)

Trọng lượng của bao xi măng là \(P=10\cdot50=500\left(N\right)\)

\(\dfrac{2}{-5}-\left(\dfrac{5}{2}-\dfrac{12}{5}\right)\)

\(=-\dfrac{2}{5}-\dfrac{5}{2}+\dfrac{12}{5}=2-\dfrac{5}{2}=-\dfrac{1}{2}\)

(53/5 + 3/4) - (9 \(\dfrac{3}{5}\) + 1/4)

= 53/5 + 3/4 - 48/5 - 1/4

= (53/5 - \48/5) + (3/4 - 1/4)

= 1 + 1/2

= 3/2