(本题满分10分,其中每小题各5分)已知:如图,在△ABC中,AB=6,BC=8,∠B=60°求:(1)△ABC的面积;(2)∠C的余弦值.
(a2+1)2-4a2
5m(x-y)2+10n(y-x)3
-8ax2+16axy-8ay2
(a+b)2-9(a-b)2
-x5y3+x3y5