Question

Ajutati-ma va rog!!!
Calculati 3a + 4b - 5c , daca stim ca a,b,c sunt invers proportionale cu nr. $\frac{1}{3}$ ; $\frac{1}{4}$ ; $\frac{1}{5}$ 

Answer 1

a,b,c invers prop cu 1/3.1/5.1/5
$\frac{a}{ \frac{1}{1/3} } = \frac{b}{ \frac{1}{1/4} } = \frac{c}{ \frac{1}{1/5} } =k$
$\frac{a}{3} = \frac{b}{4}= \frac{c}{5} =k$
a=3k
b=4k
c=5k
3*3k+4*4k-5*5k=9k+16k-25k=0