x/1 - x/5 + x/5 - x/9 +x/9 - x/13 ..... + x/53 - x/57 = 56/57

x/1 - x/57 = 56/57

56x/57 = 56/57

56x = 56

=> X = 1

Tk mình với bạn ơi. Đúng rồi nhé!!

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\(\frac{x}{1.5}+\frac{x}{5.9}+\frac{x}{9.13}+...+\frac{x}{53.57}=\frac{56}{57}\)

\(\Leftrightarrow\frac{x}{1}-\frac{x}{5}+\frac{x}{5}-\frac{x}{7}+\frac{x}{9}-\frac{x}{13}+...+\frac{x}{53}-\frac{x}{57}=\frac{56}{57}\)

\(\Leftrightarrow\frac{x}{1}-\frac{x}{57}=\frac{56}{57}\)

\(\Leftrightarrow\frac{x.57}{57}-\frac{x}{57}=\frac{56}{57}\)

\(\Leftrightarrow\frac{x.57-x}{57}=\frac{56}{57}\)

\(\Leftrightarrow\frac{x.56}{57}=\frac{56}{57}\)

\(\Leftrightarrow x=1\)

\(5^3+3^5=125+243=368\)

Thao mình thì cách nhanh nhất là BẤM MÁY TÍNH

hay nhỉ đầy đứa cùng lớp với mk đang on

8.19 = 8.(20-1) = 8.20-8 = 160-8 = 152

65.98 = 65.(100 - 2) = 65.100 - 65.2 = 6500-130 = 6370

\(\text{8.19}\)

\(=8.\left(20-1\right)\)

\(=8.20-8.1\)

\(=160-8\)

\(=152\)

\(65.98\)

\(=65.\left(100-2\right)\)

\(=65.100-65.2\)

\(=6500-130\)

\(=6370\)

a: \(\overline{3a02a}+1998\)

\(=30000+1000\cdot a+20+a+1998\)

=1001a+32018

b: \(32100-\overline{1a2a}\)

=32100-(1000+100a+20+a)

=32100-(1020+101a)

=32100-1020-101a

=-101a+31080

c: \(5001+3021+\overline{a12a}\)

=8022+1000a+120+a

=1001a+8142

d: \(\overline{56a3}-1251-5600\)

=5600+10a+3-1251-5600

=10a-1248