Question

a) Dacă a/b=2/5, calculați 7a-2b/4a+3b.
b)Știind că 7a-2b/5a+4b=2/15, calculați 10a-b/5a+b.
plzzzz. ajutoor.

Answer 1

a)
a/b = 2/5 ==> a = 2b/5
(7a - 2b)/(4a + 3b) =

= (14b/5 -2b) / (8b/5 + 3b) =

= (14b/5 - 10b/5) / (8b/5 + 15b/5) =

= 4b/5 × 5/23b =

= 4b/23b =

= 4/23

b)
(7a -2b) / (5a + 4b) = 2/15
15(7a - 2b) = 2(5a + 4b)
105a - 30b = 10a + 8b
95a = 38b |:19
5a = 2b ==> a = 2b/5

(10a - b) / (5a + b) =

= ( 20b/5 - b) / (10b/5 + b) =

= (20b/5 - 5b/5) / (10b/5 + 5b/5) =

= 15b/5 × 5/15b =

= 15b/15b =

= 1