2.10 b) a² -ac +bc -ab =a(a -c) -b(a -c) =(a -c)(a -b)(a+2b)/3(a -b) -(3c -a)/2(a-c) +(a² -bc)/(a -c)(a -b) ==(2(a-c)(a+2b) -3(a-b)(3c-a) +6(a²-bc)) /6(a-c)(a-b) ==(2(a²+2ab-ac-2bc) -3(3ac-a² -3bc+ab) +6a² -6bc) /6(a -c)(a -b) ==(2a²+4ab -2ac-4bc -9ac +3a² +9bc -3ab +6a² -6bc) /6(a -c)(a -b) ==(11a² +ab -11ac -bc) /6(a -c)(a -b) ==11a(a -c) +b(a -c)) /6(a -c)(a -b) ==(a -c)(11a +b) /6(a -c)(a -b) ==(11a +b) /6(a -b) =(11/6 -1) /6(1/6 +1) ==(11-6)/6 : 6*7/6 =5/6 : 7 =5/6 *1/7 =5/42