sinA·sinB+sinB·sinC+cos2B=1
sinAsinB+sinBsinC+1-2sinB*sinB=1
sinAsinB+sinBsinC=2sinBsinB
sinA+sinC=2sinB
a+c=2b
所以a,b,c成等差数列
2.cosC=(a^2+b^2-c^2)/2ab=-1/2
a^2+b^2-c^2=-ab
由(1)a^2+b^2-(4b^2-4ab+a^2)+ab=0
5ab-3b^2=0
所以a/b=3/5
sinA·sinB+sinB·sinC+cos2B=1
sinAsinB+sinBsinC+1-2sinB*sinB=1
sinAsinB+sinBsinC=2sinBsinB
sinA+sinC=2sinB
a+c=2b
所以a,b,c成等差数列
2.cosC=(a^2+b^2-c^2)/2ab=-1/2
a^2+b^2-c^2=-ab
由(1)a^2+b^2-(4b^2-4ab+a^2)+ab=0
5ab-3b^2=0
所以a/b=3/5