Rt△ABC中,∠C=90°,AB=10,AC=6,以C为圆心作⊙C和AB相切,则⊙C的半径长为
1-a4=___________
-a2+b2=(a+b)(______)
x(a-1)(a-2)-y(1-a)(2-a)=____________.
3(y-x)2+2(x-y)=___________
-7ab+14a2-49ab2=-7a(________).