a) 1,5 . x + 15 + x = 31
(1,5 + 1) . x + 15 = 31
2,5 .x = 31 - 15
2,5 - x = 16
x = 2,5 - 16
x = -13,5
b) (x + 1) + (x + 2) + (x + 3) + ( x + 4) + (x + 5) = 45
(x + x + x ....+ x) + (1 + 2 + 3 + 4 + 5) = 45
5x + 15 = 45
5x = 45 - 15
5x = 30
x = 6
\(50\%.x+x=52\)
\(\frac{1}{2}x+x=52\)
\(x.\left(\frac{1}{2}+1\right)=52\)
\(x.\left(\frac{1}{2}+\frac{2}{2}\right)=52\)
\(x.\frac{3}{2}=52\)
\(x=52:\frac{3}{2}\)
\(x=52.\frac{2}{3}\)
\(x=\frac{104}{3}\)
Vậy \(x=\frac{104}{3}\)
\(x-\frac{2}{3}-\frac{2}{15}-\frac{2}{35}-\frac{2}{63}=\frac{1}{9}\)
\(x-\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}\right)=\frac{1}{9}\)
\(x-\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\right)=\frac{1}{9}\)
\(x-\left(1-\frac{1}{9}\right)=\frac{1}{9}\)
\(x-1+\frac{1}{9}=\frac{1}{9}\)
\(x=\frac{1}{9}-\frac{1}{9}+1\)
\(x=1\)
Vậy \(x=1\)
\(\frac{75}{20}-x=\frac{2}{3}.10\)
\(x=\frac{75}{20}-\frac{20}{3}\)
\(x=\frac{225}{60}-\frac{400}{60}\)
\(x=-\frac{175}{60}=-\frac{35}{12}\)
Vậy \(x-\frac{35}{12}\)