#### mercury

i got them in a test..

i would appreciate it if u could tell me what i should do , or what concept is involved...

1) if a,b,c belong to the set of all real no.s and a!=b(not equal to)

then

a)a^2+b^2+ab=3c^2 for some c in (a,b)

b)a^2+b^2+ab=3c^2 for not even one c in (a,b)

c)a^2+b^2-ab=3c^2 for some c in (a,b)

2)the no. of non-negative integral solutions for the eqn.

2x+y+z=20 are

a)132

b)121

c)144

d)none of the above

thanks in advance