Ta có : B = x³ + x²y -xy² -y³ +x² -y² + 2x + 2y + 3 

               = x² (x+y+1)-y²(x + y + 1)+2(x+y+1) +2

               = x² . 0         - y² . 0          + 2. 0       + 2 

               = 2 

ta có B=x^2(x+y)-y^2(x+y)+x^2-y^2+2(x+y)+3

=)B=x^2(x+y)+x^2-y^2(x+y)-y^2+2(x+y)+2+1

=)B=x^2(x+y+1)-y^2(x+y+1)+2(x+y+1)+1

=)B=0-0+0+1=1

5^6+5^7+5^8

=5^6.(1+5+5^2)

=5^6.31 chia hết cho 31

7^6+7^5-7^4

=7^4.(7^2+7-1)

=7^4.55 chia hết cho 11

BÀI 2:

a)  \(5^6+5^7+5^8=5^6\left(1+5+5^2\right)=5^6.31\)      \(⋮\)\(31\)

b)  \(7^6+7^5-7^4=7^4.\left(7^2+7-1\right)=7^4.55\)\(⋮\)\(11\)

c)  \(2^3+2^4+2^5=2^3.\left(1+2+2^2\right)=2^3.7\)\(⋮\)\(7\)

d) mk chỉnh đề

 \(1+2+2^2+2^3+...+2^{59}\)

\(=\left(1+2\right)+\left(2^2+2^3\right)+...+\left(2^{58}+2^{59}\right)\)

\(=\left(1+2\right)+2^2\left(1+2\right)+...+2^{58}\left(1+2\right)\)

\(=\left(1+2\right)\left(1+2^2+...+2^{58}\right)\)

\(=3\left(1+2^2+...+2^{58}\right)\)\(⋮\)\(3\)

Câu a:

5.2\(^2\) + x + 3 = 5\(^2\)

5.4 + x +3 = 25

20 + x + 3 = 25

x = 25- 20 - 3

x = 5 - 3

x = 2

Vậy x = 2

Câu b:

2\(^3\) + x - 3\(^2\) = 5\(^3\) - 4\(^3\)

8 + x - 9 = 125 - 64

x = 125 - 64 + 9 - 8

x = 61 + 9 - 8

x = 70 - 8

x = 62

Vậy x = 62

a) 4.705

b) 2.05

c) 2.34

d) 6.06

a)4,705     b)2,05    c)2,34     d)6,06