A²-2a-3=(a-3)(a+1)
a1+a2=2 U a1*a2=-3⇒a=-1 U a=3
a²-5a+6=(a-3)(a-2)
a1+a2=5 U a1*a2=6⇒a1=2 U a2=3
2a²-a-2ab+b=a(2a-1)-b(2a-1)=(2a-1)(a-b)
a²-a-2=(a-2)(a+1)
a1+a2=1 U a1*a2=-2⇒a=2 U a=-1
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1)1/(a-3)(a+1) +1/(a-3)(a-2)=(a-2+a+1)/(a-3)(a+1)(a-2)=
=(2a-1)/(a-3)(a+1)(a-2)
2)(2a-1)/(a-3)(a+1)(a-2) :(a-b)(2a-1)/(a-2)(a+1)=
=(2a-1)/(a-3)(a+1)(a-2) *(a-2)(a+1)/(a-b)(2a-1)=1/(a-b)(a-3)