Calculați:
a) 2√5+3√5;
b) 4√7-3√7;
c) 1/2√3+3/4√3;
d) 3√2+2√3-2√2+3√3-√2;
e)4√11-7√13+3√13-5√11;
f)3√5-4+6-2√5-5+√5.