Question

Am nevoie de ajutor la aceste probleme urgent!
1. Un pix costa 12,8 lei. Dupa o reducere cu 25%, pretul pixului este....(cu rezolvare)
2. Solutia ecuatiei 2/3*x-1/2=1/2*x este....
3. Stiind ca media aritmetica a 4 numere este 2,5 si media aritmetica a trei dintre ele este 1,8, aflati cel de-al patrulea numar.
4. Rezolvati in multimea numerelor intregi ecuatia: xy-3x=7
Multumesc!

Answer 1

$1) 12,8= 12\frac{8}{10}= 12\frac{4}{5}= \frac{64}{5} \\ \\ 25\% \ din \ \frac{64}{25}= \frac{25}{100}* \frac{64}{5}= \frac{1}{4} * \frac{64}{5}= \frac{16}{5}= 0,64 \ -reducerea \\ \\ 12,8-0,64= \boxed{12,16- \ noul \ pret}$

$2)\frac{2x}{3}^{(2 }- \frac{1}{2}^{(3} = \frac{x}{2}^{(3} \\ \\ 4x-3=3x \\ 4x-3x=3 \\ \\ \boxed{x=3}$

$3)ma_1=\frac{a+b+c+d}{4}=2,5 \\ \\ a+b+c+d=2,5*4 \\a+b+c+d=10 \\ \\ ma_2= \frac{a+b+c}{3}=1,8 \\ \\ a+b+c=1,8*3 \\ a+b+c=5,4 \\ \\ d=10-5,4 \\ \\ \boxed{d=4,6}$

$4) xy-3x=7 \ <=> x(y-7)=7 \\ se \ face \ tabel \ si \ se \ dau \ valori \\ \\ \left[\begin{array}{ccc}x& \ &y-7 \ \ \\ \\1& \ &7\\7& \ &1 \\ -1 & \ & \ -7 \\ -7& \ & \ -1\end{array}\right] \ \\ \\ \\ 1)x=1 \ \ & \ y-7=7=>y=14 \\ \\ 2)x=7 \ \ & \ y-7=1 => y=8 \\ \\3)x=-1 \ \ & \ y-7=-7 =>y=0 \\ \\ 4)x=-7 \ \ & \ y-7=-1 =>y=6 \\ \\ \\ S_(x;y)= \{(1;14);(7;8);(-1;0);(-7;6) \}$