(rs + r) = r(s + 1)Ramit88 wrote:if r and s are integers and rs + r is always odd. which of the following must be even ?
a r
b s
c r + s
d rs - r
e r² + s
As product of r and (s + 1) is always odd, both r and (s + 1) will be always odd.
Hence, s is even and r is odd.
From this point we know that s is even and B is the correct answer as there will be only one correct answer. If you have doubt you can check the other option as follows...
Now,
- (r + s) = odd + even = odd
(rs - r) = r(s - 1) = odd*(even - 1) = odd*odd = odd
(r² + s) = odd² + even = odd + even = odd
The correct answer is B.
