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Ajutor,va rog! Explicati-mi si mie cum fac acest exercitiu.

Stiind ca x  7 , determinati valorile rapoartelor urmatoare
              - = -
              y  9


a) 5x+2y
---------
2x-y

b) x+8y
--------
3x+6y

f) 2,5+4,5x-3,5y
--------------------
0,9x+1-0,7y

d)18x-14y+25
-----------------
12+9x-7y


Răspuns :

x/y=7/9
a)(5x+2y)/(2x-y)= (5×7+2×9)/(2×7-9)=(35+18)/(14-9)=53/5

b) (x+8y)/(3x+6y)=(7+8×9)/(3 × 7+6×9)=79/75

f) (2,5+4,5x-3,5y)/(0,9x-0,7y)=(2,5+4,5×7-3,5×9)/(0,9×7-0,7×9)=
=(2,5+31,5-31,5)/(6,3-6,3)=2,5/0  fara sens

d)(18x-14y+25)/(12+9x-7y)=(18×7-14×9+25)/(12+9×7-7×9)=
 =(126-126+25)/12+63-63=25/12