Răspuns
Explicație pas cu pas:
a / b = 2 / 7
( 3 a + 2 b ) / 5 a × b = ( 3 x 2 + 2 x 7 ) / ( 5 × 2 × 7 ) = 20 / 70 = 2 / 7
sau a / 2 = b / 7 = k ⇒ a = 2 k si b = 7 k
( 3 × 2 k + 2 × 7 k ) / 5 × 2 k × 7 k =
= 20 k / 70 k² = 2 / 7 k
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a / b = 2 / 7 => 7 a = 2 b => b = 7 a / 2
( 3 a + 2 × 7 a / 2 ) / ( 5 × a × 7 a / 2 ) =
= ( 3 a + 7 a ) / ( 35 a² / 2 ) =
= 10 a × ( 2 / 35 a² ) =
= 4 / 7 a
