Question

.................................help.................... pls...........fast............22...........

Answer 1

a. (x-1)(y+1)=10
x-1=2, x=3
y+1=5, y=4

x-1=-2 x∉N
y+1=-5 y∉N

x-1=5, x=6
y+1=2, y=1

x-1=-5, x∉N
y-1=-2, y∉N

S={(3,4), (6,1)}

b. x+y=xy
x=xy-y
x=y(x-1)
y=x/(x-1), x≠1
(x-1) si x sunt numere consecutive, deci unul este par si celalalt este impar. raportul lor nu este natural decat daca unul dintre ele este =1 sau 0.
x-1=1, x=2, y=2
x=1, imposibil, am pus conditia ca x≠1
x=0, ec initiala devine 0+y=0·y, y=0
deci avem doua solutii S={(0,0), (2,2)}

c. xy-2y+3x=21
y(x-y)=21-3x
y(x-y)=3(7-x)

y=7
x-y=7-x, x-7=7-x, x=7

y=7-x
x-y=3, x-(7-x)=3, x-7+x=3, x=5, y=2
S={(5,2), (7,7)}