因为:-2abcosC=c2-a2-b2
S=c2-a2-b2+2ab=-2abcosC+2ab
以因为:s=absinC/2
所以;-2abcosC+2ab=absinC/2
sinC+4cosC=4
C=90
所以S=ab/2≤(a+b)2/8=1/2
因为:-2abcosC=c2-a2-b2
S=c2-a2-b2+2ab=-2abcosC+2ab
以因为:s=absinC/2
所以;-2abcosC+2ab=absinC/2
sinC+4cosC=4
C=90
所以S=ab/2≤(a+b)2/8=1/2