gwd18的两到数学---不会呀!!!

lingdang1988

Q36:
If x and y are integers, is y an even integer?
(1) 2y – x = x2 – y2
(2) x is an odd integer.(a)

Q22:
If –2x > 3y, is x negative?
(1) y > 0
(2) 2x + 5y – 20 = 0(d)

hedgeforfun

Q36:
If x and y are integers, is y an even integer?
(1) 2y – x = x2 – y2
(2) x is an odd integer.

first, assumed X is even, then 2y-x even, X2 even, so Y even

second,assumed x is odd, then 2y-x odd, x2 odd, so Y still even

Q22
from (1), get X<0

from (2) y=(20-2x)/5, so -2x>3/5(20-2x), so x<-15

answer is D