Question

giải bài 4 hộ mình nhé 

Answer 1

2:

a: 3x-15=30

=>3x=45

=>x=45/3=15

b: \(5x+5^2=2^4\cdot5\)

=>\(5x+25=16\cdot5=80\)

=>5x=55

=>x=11

c: \(2+x:5=6\)

=>x:5=4

=>x=4*5=20

d: \(3^x-1=26\)

=>\(3^x=26+1=27\)

=>x=3

5:

a: \(A=1+3+3^2+...+3^{101}\)

\(=\left(1+3+3^2\right)+3^3\left(1+3+3^2\right)+...+3^{99}\left(1+3+3^2\right)\)

\(=13\left(1+3^3+...+3^{99}\right)⋮13\)

b: n+4 chia hết cho n+1

=>\(n+1+3⋮n+1\)

=>\(3⋮n+1\)

=>\(n+1\in\left\{1;-1;3;-3\right\}\)

=>\(n\in\left\{0;-2;2;-4\right\}\)

mà n là số tự nhiên

nên \(n\in\left\{0;2\right\}\)