Question

Tìm x \(\in\) N , biết :

a) 16^x < 128⁴

b) 5^x . 5^{x + 1} . 5^{x + 2} < 10.....0 : 2¹⁸

                                      18 chữ số 0 

Answer 1

a)16^x<128⁴

=>(2⁴)^x<(2⁷)⁴

=>2^4x<2²⁸

<=>4x<28

<=>x<7

=>x={0;1;2;3;4;5;6}

b)5^x.5^x+1.5^x+2<100...0:2¹⁸

<=>5^3x+3<10¹⁸:2¹⁸=(10:2)¹⁸=5¹⁸

<=>3x+3<18

<=>3x<15

<=>x<5

<=>x={0;1;2;3;4}

Answer 2

a) 16^x < 128⁴

(2⁴)^x<(2⁷)⁴

2^4x<2²⁸

=>4x<28

=>x<28:4

=>x<7

mà x\(\in\)N nên

0\(\le\)x<7

b) 5^x . 5^{x + 1} . 5^{x + 2} < 10.....0 : 2¹⁸

5^x+x+1+x+2<10¹⁸:2¹⁸

5^3x+3<(10:2)¹⁸

5^3x+3<5¹⁸

=>3x+3<18

=>3x<18-3

=>3x<15

=>x<15:3

=>x<5 mà x\(\in\)N nên

0\(\le\)x<5

Answer 3

x=0;1;2;3;4;5;6

Answer 4

16^x<128^4

(2^4)^x<(2^7)^4

2^4x<2^28

x<7

=> x={0,1,2,3,4,5,6}

Answer 5

tui lam dc phan AAAAAAAAAAAAAAAA nhung ko lam dc phan BBBBB

Answer 6

mk cũng ko biết