(s-c)^2=(1/2)^2
1-2sc=1/4
sc=3/8

sc=-3/8のとき
s-c=1/2よりs=c+1/2
(c+1/2)c=-3/8
8c^2+4c+3=0
判別式D/4=2^2-8*3=-20<0