Question

ajutatima varog frumos
rezolvati in RxR    sistemul:
{3x+5y=12             
{5x-4y=-8

{x=-2y
{4x+5y-18=0

{x+y=7
{-x+7y=9

Answer 1

3x+5y=12 |inmultit cu 5
5x-4y=-8   |inm. cu -3
_______________
15x+25y=60
-15x+12y=24
___________
adunand cele 2 ecuatii obtinem
37y=84
y=84/37
3x+5.84/37=12
111x+420=74
111x=74-420=-346
x=-346/111

b)
4(-2y)+5y-18=0
-8y+5y=18
-3y=18
y=-6
x=-2y=12

c) 
x+y=7
-x+7y=9
adunand ecuatiile
x-x+y+7y=16
8y=16
y=2
x=7-y=7-2=5