已知sinA:sinB=根号2:1由正弦定理知 a:b=√2:1a=√2b (1)由余弦定理知cosB=(a^2+c^2-b^2)/2ac代入(1)得cosB=(c^2+b^2)/2√2bc=(1/2√2)(c/b+b/c) (2)由c^2=b^2+根号2bc即c/b-b/c=√2平方(c/b)^2+(b/c)^2-2=2(c/b+b/c...