Question

Dacă 6 supra x = y supra 5, determinați valoarea expresiei 128 - 3xy​

Answer 1

$\it \dfrac{6}{x}=\dfrac{y}{5} \Rightarrow xy=5\cdot6 \Rightarrow xy=30\ \ \ \ \ \ (*)\\ \\ \\ 128-3xy\ \stackrel{(*)}{=}\ 128-3\cdot30=128-90=38$

Answer 2

$\frac{6}{x} = \frac{y}{5}$

Aplicăm formula :

$\frac{a}{b} = \frac{c}{d} < = > a \times d = b \times c$

$\frac{6}{x} = \frac{y}{5} < = > x \times y = 6 \times 5 = > x \times y = 30$

$128 - 3xy = 128 - (3 \times 30) = 128 - 90 = \huge \boxed{ \red{38} } {}$