4. Calculați: x-y-z, x+y-z şi-x - y + z, unde x = a + b -c, y = a-b-c şi
z=-a-b+c, iar:
a) a=5√5-3√2+2√3, b= √5-4√2-3√3, c= 2√5-√3-5√2;
b) a=6√5-5√2-4√3,6=3√5-4√2-6√3, c= -√5 +2√3-6√2;
c) a = 4√5-7√2-3√3, b=-2√5 +5√2-7√3, c=-3√5-3√2-5√3.