3C=3^4+3^5+...+3^2019

=>2C=3^2019-3

=>\(C=\dfrac{3^{2019}-3}{2}\)

mình làm theo cách lớp 12 nhé 

a: \(=\left\{145-\left[130-10\right]:2\right\}\cdot5\)

\(=\left\{145-60\right\}\cdot5=85\cdot5=425\)

b: \(=100:\left\{250:\left[450-4\cdot125+4\cdot25\right]\right\}\)

\(=\dfrac{100}{250:\left[450-500+100\right]}=\dfrac{100}{250:50}=\dfrac{100}{5}=20\)

c: \(=355-5\cdot\left[64-\left(27-25\right)\right]=355-5\cdot\left[64-2\right]\)

\(=355-310=45\)

\(\left(x+1\right)^3=27\)

\(\left(x+1\right)^3=3^3\)

\(\Rightarrow x+1=3\)

\(x=2\)

\(\left(x+1\right)^3=27\)

\(< =>\left(x+1\right)^3=3.3.3=3^3\)

\(< =>x+1=3< =>x=3-1=2\)

\(\left(2x+3\right)^3=9.81\)

\(< =>\left(2x+3\right)^3=9.9.9\)

\(< =>\left(2x+3\right)^3=9^3\)

\(< =>2x+3=9< =>2x=6\)

\(< =>x=\frac{6}{2}=3\)

ai giúp mình với 

các góc nhọn,tù,vuông có bao nhiêu độ

a)\(A=1+3+3^2+...+3^{2018}\)

\(\Rightarrow3A=3.\left(1+3+3^2+...+3^{2018}\right)\)

\(\Rightarrow3A=3+3^2+3^3+...+3^{2019}\)

\(\Rightarrow3A-A=3+3^2+3^3+...+3^{2019}-\left(1+3+3^2+...+3^{2018}\right)\)

\(\Rightarrow2A=3^{2019}-1\)

\(\Rightarrow A=\frac{3^{2019}-1}{2}\)

b) \(B=5+5^2+...+5^{2017}\)

\(\Rightarrow5B=5^2+5^3+...+5^{2018}\)

\(\Rightarrow5B-B=5^2+5^3+...+5^{2018}-5-5^2-...-5^{2017}\)

\(\Rightarrow4B=5^{2018}-5\)

\(\Rightarrow B=\frac{5^{2018}-5}{4}\)

a,A=1+3+3²+...+3²⁰¹⁷

3A=3+3²+3³+...+3²⁰¹⁸

3A-A=3²⁰¹⁸-1

2A=3²⁰¹⁸-1

A=(3²⁰¹⁸-1):2

Sai đề câu E sửa lại 95 hoặc 93 vì đây là dãy số mũ lẻ. Ta có : 

\(E=3+3^3+3^5+3^7+...+3^{95}\)

\(\Rightarrow\) \(9E=3^3+3^5+3^7+3^9+...+3^{95}+3^{97}\)

\(\Rightarrow\) \(8E=3^{97}-3\)

\(\Rightarrow\) \(E=\frac{3^{97}-3}{8}\)

\(E=3+3^3+3^5+3^7+.......+3^{95}\)

\(\Rightarrow9E=3^3+3^5+3^7+3^9+...+3^{97}\)

\(\Rightarrow9E-E=\left(3^3+3^5+3^7+3^9+....+3^{97}\right)-\left(3+3^3+3^5+3^7+.....+3^{95}\right)\)

\(\Rightarrow8E=3^{97}-3\)

\(\Rightarrow E=\frac{3^{97}-3}{8}\)

\(F=1+2018+2018^2+......+2018^{2017}\)

\(=2018^0+2018^1+2018^2+....+2018^{2017}\)

\(\Rightarrow2018F=2018^1+2018^2+2018^3+....+2018^{2018}\)

\(\Rightarrow2018F-F=\left(2018^1+2018^2+2018^3+....+2018^{2018}\right)-\left(2018^0+2018^1+2018^2+....+2018^{2017}\right)\)

\(\Rightarrow2017F=2018^{2018}-1\)

\(\Rightarrow F=\frac{2018^{2018}-1}{2017}\)

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

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

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