Răspuns:
Explicație pas cu pas:
x/y = 2/5 ⇒ 5 x = 2 y ⇒ x/2 = y/5 = k → coeficient de proportionalitate
⇒ x = 2 k si y = 5 k
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( 5 x + y ) / ( 3 x - y ) = 15
= ( 5 × 2k + 5 k ) / ( 3 × 2 k - 5 k ) =
= ( 10 k + 5 k ) / ( 6 k - 5 k ) =
= 15 k / k =
= 15 /1 =
= 15
