Ta có

30 + 29 + 28 + 27 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5).x

(30.31):2 = 15.x

465 = 15x

x = 465 : 15

x = 31

Vậy x = 31 là giá trị cần tìm

Theo bài ra ta có:
30 + 29 + 28 + ... + 2 + 1 = (1 + 2 + 3 + 4 + 5) . x
(30 + 1) x 30 : 2 = 15 . x
x = 465 : 15
x = 31

\(30+29+28+...+2+1=\left(1+2+3+4+5\right).x\)

\(30+29+28+...+2+1\)

Có số số là: \(\left(30-1\right):1+1=30\) (số)

Tổng: \(\left(30:2\right).\left(30+1\right)=465\)

\(\Rightarrow\left(1+2+3+4+5\right).x=465\)

\(15.x=465\)

\(x=465:15\)

\(\Rightarrow x=31\)

Vậy \(x=31\)

ai trả lời câu hỏi này ko

a)15/16:3/8x3/4

=15/16:6/16x12/16

=15/16x16/6x12/16

=15/6x12/16

=30/16=15/8

b)5/11x18/29-5/11x8/29+5/11x19/29

=5/11x(18/29-8/29+19/29)

=5/11x1=5/11

mik cũng cần gấp

vòng 19 đúng ko

|x| - 7 = 11

<=> |x| = 18

<=> x = 18

hoặc x = -18

Vậy...

a)\(\frac{2}{7}\)= \(\frac{4}{14}\)= \(\frac{6}{21}\)=\(\frac{8}{28}\)= ...

vì 5 < y < 29 \(\Rightarrow\)\(\frac{x}{y}\)= \(\frac{4}{14}\)= \(\frac{6}{21}\)= \(\frac{8}{28}\)

b)\(\frac{28}{8}\)= \(\frac{7}{2}\)= \(\frac{14}{4}\)= \(\frac{21}{6}\)= \(\frac{35}{10}\)= ...

vì 1 < y < 10\(\Rightarrow\)\(\frac{x}{y}\)= \(\frac{14}{4}\)= \(\frac{21}{6}\)

\(\dfrac{4}{5}x-x-\dfrac{3}{2}x+\dfrac{4}{3}=\dfrac{1}{2}-\dfrac{6}{5}\\ \Rightarrow\left(\dfrac{4}{5}-1-\dfrac{3}{2}\right)x=-\dfrac{7}{10}-\dfrac{4}{3}\\ \Rightarrow-\dfrac{17}{10}x=\dfrac{-61}{30}\\ \Rightarrow x=\dfrac{61}{51}\)

\(\Leftrightarrow x\cdot\dfrac{-17}{10}=\dfrac{1}{2}-\dfrac{6}{5}-\dfrac{4}{3}=\dfrac{-61}{30}\)

hay x=61/51