ko bit

a, 20^2 - 6^ 2=  400 - 36 = 364

b,3^3 . 18 - 3^3 . 12 = 3^3 . ( 18-12) = 27 . 6 = 162

c, 39 . 213 + 87 . 39 = ( 213 + 87) . 39 = 300 . 39 = 110700

d, 80 - [ 130 - ( 12 - 4)^2] = 80 - [130 - (3^2) ] = 80 - 130 - 9 = -59

A=5 296 163 666_x10¹⁵

\(a,3^6:3^5=3^{6-5}=3\\ b,5^7:5^5=5^{7-5}=5^2=25\\ c,14^5:2^3:7^4=\left(2^5:2^3\right)\cdot\left(7^5:7^4\right)=2^2\cdot7=28\\ d,5^4-2\cdot5^3=5^3\left(5-2\right)=3\cdot5^3=375\)

a) 3^6 : 3^5 = 729 : 243 = 3

b) 5^7 : 5^5 = 78125 : 3125 = 25

c) 14^5 : 2^3 : 7^4 = 537824 : 8 : 2401 = 89

d) 5^4 - 2 * 5^3 = 625 - 2 * 125 = 625 - 250 = 375

\(a,3^6:3^5=3^{6-5}=3^1=3\\ b,5^7:5^5=5^{7-5}=5^2=25\\ c,14^5:2^3:7^4=\left(2^5:2^3\right).\left(7^5:7^4\right)=2^{5-3}.7^{5-4}=2^2.7^1=4.7=28\\ d,5^4-2.5^3=5.5^3-2.5^3=\left(5-2\right).5^3=3.5^3=3.125=375\)

\(\Rightarrow2S=6+\frac{3}{1}+\frac{3}{2}+...+\frac{3}{2^8}\)

\(\Rightarrow2S-S=\left(6+3+\frac{3}{2}+...+\frac{3}{2^8}\right)-\left(3+\frac{3}{2}+...+\frac{3}{2^9}\right)\)

\(\Rightarrow S=3-\frac{3}{2^9}\)

\(S=3+\frac{3}{2}+\frac{3}{2^2}+\frac{3}{2^3}+...+\frac{3}{2^9}\)

\(\Rightarrow\frac{1}{2}.S=\frac{3}{2}+\frac{3}{2^2}+\frac{3}{2^3}+...+\frac{3}{2^{10}}\)

\(\Rightarrow S-\frac{1}{2}.S=\frac{1}{2}.S=3+\frac{3}{2}+\frac{3}{2^2}+\frac{3}{2^3}+...+\frac{3}{2^9}-\left(\frac{3}{2}+\frac{3}{2^2}+\frac{3}{2^3}+...+\frac{3}{2^{10}}\right)\)

\(\Rightarrow\frac{1}{2}.S=3-\frac{3}{2^{10}}\)

\(\Rightarrow S=6-\frac{6}{2^{10}}\)

a, -17

b,- 13,4

c,-68

d,700000

các bạn giải chi tiết hộ mình nhé

Bài 2:

\(3A=3+3^2+...+3^{101}\)

=>2A=3^101-1

=>\(A=\dfrac{3^{101}-1}{2}\)