31

 = 31

5 x 6 + 1 = 31

7 + 5 x 6 +7

= 7 + 30 +7

= 37 + 7

= 44

= 7+30+7

=37+7

44

7+5x6+7

=7+30+7

=37+7

=44

5x6-3x4+10

= 30-12+10

=30+10-12

=40-12=28

28 bạn ạ

28 nho 

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{6}-\dfrac{1}{7}=\dfrac{1}{2}-\dfrac{1}{7}=\dfrac{5}{14}\)

\(=\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{20}-\dfrac{1}{21}=\dfrac{21-2}{42}=\dfrac{19}{42}\)

Lời giải:
Gọi biểu thức số 1 là A và số 2 là B

\(A=\frac{3-2}{2\times 3}+\frac{4-3}{3\times 4}+\frac{5-4}{4\times 5}+\frac{6-5}{5\times 6}+\frac{7-6}{6\times 7}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)

\(=\frac{1}{2}-\frac{1}{7}=\frac{5}{14}\)

B tương tự A:
\(B=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{20}-\frac{1}{21}\)

\(=\frac{1}{2}-\frac{1}{21}=\frac{19}{42}\)

9/5 x6/65=54/325

cai nay = 54/325

dễ ợt

=54/325

2+x=5x6

=>2+x=30

=>x=30-2

=>x=28

2 + x = 5 x 6

2 + x = 30

x = 30 - 2

x = 28

2 + x = 5x6.

2 + x = 30.

      x = 30 - 2

      x = 28.

T-i-k mk thì mk t-i-k lại

= 2 + 12 +20 +30
= 14 + 20 + 30
= 34 + 30
= 64

1x2+3x4+4x5+5x6

=2+12+20+30

=14+20+30

=34+30

=64

=2+12+20+30

=64