Question

daca a supra b = cu 2 supra 7 ,atunci 3 a+2 b supra 5a-b=​

Answer 1

Răspuns:

Explicație pas cu pas:

a/b=2/7

=>a=2b/7

3a+2b/5a-b= 3x2b/7 + 2b /5x2b/7-b

=6b/7+2b / 10b/7-b

6b+14b/7 /10b-7b/7

20b/7 /3b/7

20b/7 x 7/3b= 20/3

Answer 2

Răspuns:

Explicație pas cu pas:

a/b = 2/7  ⇒  a = 2  si b = 7

( 3a+2b)/(5a-b) = 20/3

= (3×2+2×7)/(5×2-7) =

= (6+14)/(10-7)=

= 20/3

_________________________

• Sau:

a/b = 2/7 =>  7 a = 2 b =>  a/2 = b/7 = k -> coeficient de proportionalitate

=>  a = 2 k   si b = 7 k

(3a+2b)/(5a-b) = 20/3

= (3×2k + 2×7k) /(5×2k - 7k) =

= (6k+14k)/(10k-7k) =

= 20k/3k =  

= 20/3