123.456+123.789-1245.23

=123.(456+789)-1245.23

=123.1245-1245.23

=1245.(123-23)

=1245.100

=124500

=123.(456+789)-1245.23

=123.1245-1245.23

=1245.(123-23)

=1245.100

=124500

a)(bạn kia làm rồi)

b)2^9:16^2+81^5:3^18-125^7:625^5

=2^9:(2^4)^2+(3^4)^5:3^18-(5^3)^7:(5^4)^5

=2^9:2^8+3^20:3^18-5^21:5^20

=2+3^2+5

=2+9+5

=16

2⁹ : 16² + 81⁵ : 3¹⁸ - 125⁷ : 625⁵

= 2⁹ : ( 2⁴ )² + ( 3⁴ )⁵ : 3¹⁸ - ( 5³ )⁷ : ( 5⁴ )⁵

= 2⁹ : 2⁸ + 3²⁰ : 3¹⁸ - 5²¹ : 5²⁰

= 2 + 3² - 5

= 2 + 9 - 5

= 6

16^2=(2^4)^2=2^8

81^5=(3^4)^5=3^20

125^7=(5^3)^7=5^21

625^5=(5^4)^5 =5 ^20

TA CÓ  2^9/ 16^1+81^4/3^18-125^7/625^5

=2^9/2^8+3^20/3^18-5^21/5^20

=2+3 ^ 2 -5

=2+9-5

=11-5=6

\(2^9\div16^2+81^5\div3^{18}-125^7\div625^5\)

\(=2^9\div\left(2^4\right)^{^2}+\left(3^4\right)^{^5}\div3^{18}-\left(5^3\right)^{^7}\div\left(5^4\right)^{^5}\)

\(=2^9\div2^8+3^{20}\div3^{18}-5^{21}\div5^{20}\)

\(=2^1+3^2-5^1\)

\(=2+9-5\)

\(=6\)

A) 11/125+(-17/18+4/9)-(5/7-17/14)

 =11/125+(-17/18+8/18)-(10/14-17/14)

=11/125+(-1/2)-(-1/2)

=11/125

B)(1+2+3+4-3-2-1)-(1/2+1/2+2/3+1/3+3/4+1/4)

 =4-3

=1

à bn lấy trong sách các dạng toán và phương pháp giải hả

81 : 3^2 + 5 x 3

= 81 : 9 + 5 x 3

= 9 + 5 x 3

= 9 + 15

= 24

81 : 3^2 + 5 x 3 = 3^4 : 3^2 + 5 x 3

                        = 3^2 + 15 = 9 + 15 = 24

\(\infty\)