Question

câu 1: tìm x
a) 1+3+5+7+......+ (2x+1) = 225
b) 130-[ 5.(9-x)+43] =47
c) 16 mũ x < 32 mũ 4

Answer 1

a.1+3+5+7+...+2x+1=225

[(2x+1-1):2+1]x(2x+1+1):2=225

(x+1)x(2x+2):2=225

(x+1)x(x+1)=225

(x+1)²=225

(x+1)²=15²

x+1=15

x=14

_______________

b. 130-[5.(9-x)+43]=47

    5.(9-x)+43=83

  5.(9-x)=40

9-x=8

x=1

_______________

c.16^x<32⁴

2^4x<2²⁰

=>x∈{0;1;2;3;4}

Answer 2

a: =>(x+1)^2=225

=>x+1=15

=>x=14

b: =>[5*(9-x)+43]=130-47=83

=>5(9-x)=40

=>9-x=8

=>x=1

c: =>2^4x<2^20

=>4x<20

=>0<x<5