Question

1Tìm x

a.2^3x+1=128

b.(7x-11)³=2⁵+5²+200

c.(2x+1)+(2x+2)+(2x+3)+...+(2x+101)=5757

 

Answer 1

a.2^3x+1=128

=> 2^{3x + 1} = 2⁷

=> 3x + 1 = 7

=> 3x = 6

=> x = 2

vay_

Answer 2

a.2^3x +1=128

= 2^3x x 2=128

 =128:2=64=2 mũ 6

vậy x=2

b.(7x-11)³=2⁵+5²+200

(7x-11)³=257=6,3579 mũ 3

7x=17,3579

x=2,4797

c.(2x+1)+(2x+2)+(2x+3)+...+(2x+101)=5757

vế trái có 101 số hạng

VT =(2x +1+2x+101).101:2=(4x+102).101:2=5757

(4x+102).101 =5757.2=11514

(4x+102)=11514:101=114

4x=114-102=12

x=12:4=3

vậy x=3