Question

Determinati x e R

5x   =    20
4             x

Answer 1

5x²=80
x²=80/5
x²=16
x=√16
x=4

Answer 2

Folosind proprietatea fundamentala a proporțiilor
$\dfrac{5x}{4}=\dfrac{20}{x}\Rightarrow 5x^2=80\Rightarrow x^2=16\Rightarrow x_{1;2}=\pm4$