Question

4) Câte numere naturale verifică relația: 2,1x + 1,2 < 7,5? R=?
Scrieți rezolvări complete:

Answer 1

2,1x + 1,2 < 7,5

2,1x < 7,5-1,2

2,1x < 6,3

x < 63/10 : 21/10

x < 63/10 * 10/21

x < 3

x apartine {0,1,2}

Answer 2

$\it 2,1x+1,2 < 7,5\Big|_{\cdot10} \Rightarrow21x+12 < 75\Big|_{:3} \Rightarrow 7x+4 < 25\Big|_{-4} \Rightarrow \\ \\ \\ \Rightarrow 7x < 21|_{:7} \Rightarrow x < 3\ \stackrel{x\in\mathbb{N}}{\Longrightarrow}\ x\in\{0,\ \ 1,\ \ 2\}$