My cousin sings better than I do.

3M=1+1/3+1/9+...+1/2187

2M=3M-M

2M=1-1/6561

2M=6560/6561

M=3280/6561

b,(1+2/3-1/4).(4/5-3/4)²

=(5/3-1/4).(1/20)²

=17/12.1/400

=17/4800

c,2:(4/3-16/15)² -12

=2:(4/15)²-12

=2:16/225-12

=225/8-12

=129/8

g,\(\dfrac{10^3+5.10^2+5^3}{-13}\)

=\(\dfrac{1625}{-13}\)

câu b cái mũ bạn tô đen là bạn gạch đi hay là cái mũ nào đấy

a,(3/5+1/2)²-(3/4-5/6)

=121/100-1/144

=4331/3600

c,\(\dfrac{6^2.6^3}{2^53^5}\)

=\(\dfrac{6^5}{6^5}\)=1

d,\(\dfrac{2^7.9^3}{6^5.8^2}\)

=\(\dfrac{2^7.3^6}{2^5.3^5.2^6}\)

=\(\dfrac{3}{16}\)

thì 3M là gấp 3 lần M lên đấy VD:

1/3 nhân 3 thì bằng 1

3M=1+1/3+1/9+...+1/2187

2M=3M-M

2M=1-1/6561

2M=6560/6561

M=3280/6561

3M=1+1/3+1/9+...+1/2187

2M=3M-M

2M=1-1/6561

2M=6560/6561

M=3280/6561

x : 3/5 = 1/2

x         = 1/2 x 3/5

x        =      3/10

x : 5/7 = 3/8

x         = 3/8 x 5/7

x          =   15/56

x : 1/3 = 4/7

x         =  4/7 x 1/3