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x+x:5*7,5+x:2*9=315
x*1+x*3/2+x*9/2=315
x*(1+3/2+9/2)=315
x*7=315
x=315:7
x=45
X + X x ( 7,5 : 5 ) + X x ( 9 : 2 ) = 315
X x 1 + X x 1,5 + X x 4,5 = 315
X x ( 1 + 1,5 + 4,5 ) = 315
X x 7 = 315
X = 315 : 7
X = 45
\(\left(\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right).y=\frac{2}{3}\)
\(\frac{1}{2}.\left(1-\frac{1}{3}\right)+\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}\right)+\frac{1}{2}.\left(\frac{1}{5}-\frac{1}{7}\right)+\frac{1}{2}.\left(\frac{1}{7}-\frac{1}{9}\right)+\frac{1}{2}.\left(\frac{1}{9}-\frac{1}{11}\right).y=\frac{2}{3}\)
\(\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right).y=\frac{2}{3}\)
\(\frac{1}{2}.\left(1-\frac{1}{11}\right).y=\frac{2}{3}\)
\(\left(1-\frac{1}{11}\right).y=\frac{4}{3}\)
\(\frac{10}{11}.y=\frac{4}{3}\)
\(\Rightarrow y=\frac{22}{15}\)
a) \(2075:5=\frac{x\times75}{5+40}\)
\(415=\frac{x\times75}{45}\)
\(\Rightarrow x\times75=415\times45\)
\(x\times75=18675\)
\(x=18675:75\)
\(x=249\)
b) \(x+x:5\times7,5+x:2\times9=315\)
\(x+x\times\frac{1}{5}\times7,5+x\times\frac{1}{2}\times9=315\)
\(x\times\left(1+\frac{1}{5}\times7,5+\frac{1}{2}\times9\right)=315\)
\(x\times7=315\)
\(x=315:7\)
\(x=45\)
Lưu ý mình dùng * thay cho dấu nhân và / thay cho dấu chia.
a) 2075/5 = \(\frac{x\cdot75}{5+40}\)
\(\frac{x\cdot75}{5+40}\) = \(\frac{x\cdot75}{45}\) = 415
(x * 75) / 45 = 415
x * 75 = 415 * 45 = 18675
x = 18675 / 75
x = 249
b) x + x / 5 * 7,5 + x / 2 * 9 = 315
x + x * \(\frac{7,5}{5}\)+ x * \(\frac{9}{2}\)= 315
x * 1 + x * \(\frac{7,5}{5}\)+ x * \(\frac{9}{2}\)= 315
x * (1 + \(\frac{7,5}{5}\)+ \(\frac{9}{2}\)) = 315
x * 7 = 315
x = 315 / 7
x = 45
Chúc bạn học tốt !