Đổi hai gặp được số con hạc là:

2+1=3(con)

Đáp số:3 con.

\(\frac{2^2}{1.3}.\frac{3^2}{2.4}.\frac{5^2}{3.5}.\frac{4^2}{4.6}\)

\(=\frac{2^2.3^2.5^2.4^2}{1.3.2.4.3.5.4.6}\)

\(=\frac{2^2.3^2.4^2.5^2}{1.2.3^2.4^2.5.6}\)

\(=\frac{2.5}{6}\)

\(=\frac{10}{6}=\frac{5}{2}\)

a, 2012 : x + 23 = 526

2012 : x = 526 - 23 

2012 : x = 503

x = 2012 : 503 

x = 4

b , ( x - 1/2 ) x 5/2 + 1/2 = 7/4

( x - 1/2 ) x 5/2 = 5/4

x - 1/2 = 5/4 : 5/2 

x -1/2 = 1/2

x = 1/2 + 1/2

x = 1

a) 2012 : x + 23 = 526

=> 2012 : x = 526 - 23 = 503

=> x = 2012 : 503 = 4

c) (x - 1/2) x 5/2 + 1/2 = 7/4

       (x - 1/2 ) x 5/2 = 7/4 - 1/2 = 5/4

=> x - 1/2 = 5/4 : 5/2 = 1/2

   => x = 1/2 + 1/2 = 1

=> x = 1

\(P=\frac{1}{2.3}+\frac{1}{6.5}+............+\frac{1}{198.101}\)

\(P=\frac{1}{6}+\frac{1}{30}+.........+\frac{1}{19998}\)

\(\frac{1}{2}P=\frac{1}{12}+\frac{1}{60}+...........+\frac{1}{39996}\)

\(\frac{1}{2}P=\frac{1}{2.6}+\frac{1}{6.10}+.........+\frac{1}{198.202}\)

\(\frac{1}{2}P=\frac{1}{4}.\left(\frac{4}{2.6}+\frac{4}{6.10}+..........+\frac{4}{198.202}\right)\)

\(\frac{1}{2}P=\frac{1}{4}.\left(\frac{1}{2}-\frac{1}{6}+\frac{1}{6}-\frac{1}{10}+..........+\frac{1}{198}-\frac{1}{202}\right)\)

\(\frac{1}{2}P=\frac{1}{4}.\left(\frac{1}{2}-\frac{1}{202}\right)\)

\(\frac{1}{2}P=\frac{1}{4}.\frac{50}{101}\)

\(\frac{1}{2}P=\frac{25}{202}\)

\(P=\frac{25}{202}:\frac{1}{2}\)

\(P=\frac{25}{101}\)

có số lời chào là:

     10 x 10 = 100 ( lời chào )

                 Đáp số : 100 lời chào

Co 90 loi chao

1,a) (x-1)(x^2+x+1)=x^3-1

VT=x³+x²+x-x²-x-1

=(x³-1)+(x²-x²)+(x-x)

=x³-1+0+0

=x³-1=VP (dpcm)