a, 6¹⁰⁰ - 1 = (6 . 6 . 6 ..... 6) - 1 = [(...6) . (...6) . (...6) ..... (...6)] - 1 = (...6) - 1 = ...5 \(⋮\) 5

b, 21²⁰ - 11¹⁰ = (21 . 21 . 21 . 21 . 21..... 21) - (11 . 11 . 11 . 11 ..... 11) = [(...1) . (...1) . (...1) . (...1).....(...1)] - [(...1) . (...1) . (...1) . (...1).....(...1)] = (...1) - (...1) = ....0 \(⋮\) 2; \(⋮\) 5

mình cảm ơn ạ

Đặt \(A=6^2+6^4+6^6+...+6^{98}+6^{100}\)

Ta có: \(A=6^2+6^4+6^6+...+6^{98}+6^{100}\)

\(\Leftrightarrow36A=6^4+6^6+...6^{100}+6^{102}\)

\(\Leftrightarrow A-36A=6^2+6^4+6^6+...6^{98}+6^{100}-6^4-6^6-...-6^{100}-6^{102}\)

\(\Leftrightarrow-35\cdot A=6^2-6^{102}\)

\(\Leftrightarrow A=\dfrac{6^{102}-6^2}{35}\)

     C = 1 + 6 + 6²+ 6³+...+ 6¹⁰⁰

     6C =      6 + 6²+ 6³ +...+ 6¹⁰⁰ + 6¹⁰¹

6C - C =  6¹⁰¹ - 1

        5C = 6¹⁰¹ - 1

           C = \(\dfrac{6^{101}-1}{5}\)

\(C=1+6+6^2+...+6^{100}\)

\(\Rightarrow C=\dfrac{6^{100+1}-1}{6-1}\)

\(\Rightarrow C=\dfrac{6^{101}-1}{5}\)

a ,   400 + 3 + 8 1000 = 400 + 3 + 0 , 008 = 403 + 0 , 008 = 403 , 008 b , 65 + 0 , 7 + 0 , 003 = 65 , 7 + 0 , 003 = 65 , 703 c , 210 + 5 + 0 , 35 = 215 + 0 , 35 = 215 , 35 d , 170 + 9 + 6 100 + 3 10 = 170 + 9 + 0 , 06 + 0 , 3 = 179 + 0 , 06 + 0 , 3 = 179 , 06 + 0 , 3 = 179.36

Đáp án đúng là:0,06

a) 

400 + 3 + 8 1000 = 400 + 3 + 0 , 008 = 403 + 0 , 008 = 403 , 008

b)

65 + 0 , 7 + 0 , 003 = 65 , 7 + 0 , 003 = 65 , 703

c)

210 + 5 + 0 , 35 = 215 + 0 , 35 = 215 , 35

d)

170 + 9 + 6 100 + 3 10 = 170 + 9 + 0 , 06 + 0 , 3 = 179 + 0 , 06 + 0 , 3 = 179 , 06 + 0 , 3 = 179.36

0,06

Đáp án B

a, 6100 + 2900

 = (6000 + 2000) + (100 + 900)

 = 8000 + 1000 = 9000

b, 7825 + 1075

 = (7000 + 1000) + 800 + (25 + 75)

 = 8000 + 800 + 100

 = 8900

c, 285 + 285 + 285 + 285 = 285 × 4 = 1140

d, 2345 + 1745

 = (2000 + 1000) + (300 + 700) + (45 + 45)

 = 3000 + 1000 + 90

 = 4090