Cậu 1: \(4^3\cdot4^n=16^2\)

\(\Rightarrow4^3\cdot4^n=4^4\) \(\Rightarrow4^n=\frac{4^4}{4^3}=4^1\) \(\Rightarrow n=1\)

Câu 2: \(8^5:2^n=16^2\)

\(\Rightarrow2^{15}:2^n=2^8\) \(\Rightarrow2^n=\frac{2^{15}}{2^8}=2^7\) \(\Rightarrow n=7\)

Phần b bạn viết sai đề sửa lại không biết đúng không.

~~ HT ~~

Câu 1:

\(4^3\times4^n=16^2\)

\(4^{3+n}=16^2\)

\(4^{3+n}=4^4\)

\(\Rightarrow3+n=4\)

\(\Rightarrow n=4-3\)

\(\Rightarrow n=1\)

Câu 2 hình như sai đề

HOK TỐT !!! NHỚ CHO MIK 

Lời giải:

8A=(3^2-1)(3^2+1)(3^4+1)(3^8+1)(3^{16}+1)-4.3^{32}$

$=[(3^2-1)(3^2+1)](3^4+1)(3^8+1)(3^{16}+1)-4.3^{32}$

$=(3^4-1)(3^4+1)(3^8+1)(3^{16}+1)-4.3^{32}$

$=(3^8-1)(3^8+1)(3^{16}+1)-4.3^{32}$

$=(3^{16}-1)(3^{16}+1)-4.3^{32}$

$=3^{32}-1-4.3^{32}$

$=-3.3^{32}-1=-3^{33}-1$
$\Rightarrow A=\frac{-3^{33}-1}{8}$

Program HOC24;

var a: real;

i,n: integer;

begin

write('Nhap n='); readln(n);

a:=0;

for i:=1 to n do a:=a+1/i;

write('A= ',a);

readln

end.

ta có

A = \(1+\frac{1+2}{2}+\frac{1+2+3}{3}+\frac{1+2+3+4}{4}+......+\frac{1+2+3+\text{4 +....+16}}{16}\)

xét tổng S = 1+2+3+4+5+......+n  = \(\frac{\left(n+1\right)n}{2}\) lấy \(\frac{S}{n}=\frac{\frac{\left(n+1\right)n}{2}}{n}=\frac{n+1}{2}\)

ta có

A=\(1+\frac{\frac{2\left(2+1\right)}{2}}{2}+\frac{\frac{3\left(3+1\right)}{2}}{3}+\frac{\frac{4\left(4+1\right)}{2}}{4}+\frac{\frac{5\left(5+1\right)}{2}}{5}+......+\frac{\frac{16\left(16+1\right)}{2}}{16}\)

A = \(1+\frac{1+2}{2}+\frac{1+3}{2}+\frac{1+4}{2}+\frac{1+5}{2}+......+\frac{1+16}{2}\)

A = \(1+\frac{1+2+1+3+1+\text{4+1+5+1+6+.....+1+16}}{2}\)

A = \(1+\frac{151}{2}\)

A = \(\frac{153}{2}\)

bằng 76 mới đúng

a) (2x - 1)(x^2 - 1 + 1) = 2x^3 - 3x^2 + 2

(2x - 1).x^2 = 2x^3 - 3x^2 + 2

2x^3 - x^2 = 2x^3 - 3x^2 + 2

-x^2 = -3x^2 + 2

2x^2 = 2

x^2 = 1

=> x = 1; -1

b) (x + 2)(x + 2) - (x - 2)(x - 2) = 8x

(x + 2)^2 - (x - 2)^2 = 8x

x^2 + 4x + 4 - x^2 + 4x - 4 = 8x

8x = 8x

=> x thuộc N*

c) (x + 1)(x + 2)(x + 5) - x^3 - 8x^2 = 27

x^3 + 5x^2 + 2x^3 + 10x + x^2 + 5x + 2x + 10x - x^3 - x^2 = 27

17x + 10 = 27

17x = 27 - 10

17x = 17

=> x = 1

d) (x + 1)(x^2 + 2x + 4) - x^3 - 3x^2 + 16 = 0

x^3 + 2x^2 + 4x + x^2 + 2x + 4 - x^3 - 3x^2 + 16 = 0

6x + 20 = 0

6x = -20

x = -20/6

=> x = -10/3