Question

7. Determinați numarul necunoscut din proporțiile:
b )x -5 supra 4 egal 7 supra 2
c) 3 supra 5 egal 2x -7 supra 9
d) 3x+4 supra 7 = 11 supra 5
e) 5x +1 supra 2 = 4 supra 3

Cine stieeee?​

Answer 1

b)

$\frac{x - 5}{4} = \frac{7}{2}$

(x-5)×2=4×7

2x-10=28 /+10

2x=38

x=19

c)

$\frac{3}{5} = \frac{2x - 7}{9}$

5×(2x-7)=3×9

10x-35=27 /+35

10x=62

$x = \frac{62}{10} = \frac{31}{5}$

d)

$\frac{3x + 4}{7} = \frac{11}{5}$

(3x+4)×5=7×11

15x+20=77 /-20

15x=57

$x = \frac{57}{15} = \frac{19}{5}$

e)

$\frac{5x + 1}{2} = \frac{4}{3}$

(5x+1)×3=2×4

15x+3=8 /-3

15x=5

$x = \frac{5}{15} = \frac{1}{3}$

!produsul mezilor este egal cu produsul extremilor!

Answer 2

Răspuns:

$b)\:\:\it\dfrac{x-5}{4}=\dfrac{7}{2}\Rightarrow 2\cdot(x-5) = 4\cdot7\Rightarrow2x-10=28\Rightarrow 2x = 38\Rightarrow\boxed{\it x=19}\\\\\\c)\:\:\:\it\dfrac{3}{5}=\dfrac{2x-7}{9}\Rightarrow 5\cdot(2x-7) = 3\cdot9\Rightarrow10x-35=27\Rightarrow 10x = 62\Rightarrow\boxed{\it x=\dfrac{31}{5}}\\\\\\ d)\:\:\it\dfrac{3x+4}{7}=\dfrac{11}{5}\Rightarrow5(3x+4)=11\cdot7\Rightarrow 15x+20=77\Rightarrow 15x=57\Rightarrow\\\\\boxed{\it x=\dfrac{19}{5}}$

$e)\:\:\it\dfrac{5x+1}{2}=\dfrac{4}{3}\Rightarrow 3\cdot(5x+1) = 4\cdot2\Rightarrow15x+3=8\Rightarrow 15x=5\Rightarrow\boxed{\it x=\dfrac{1}{3} }$