Question

已知sina+sinb=1,求cosa+cosb的取值范围.

Answer 1

sinA+sinB=1……(1)

设cosA+cosB=S……(2)

(1)^2+(2)^2:1+1+2(cosAcosB+sinAsinB)=S^2+1

--->2+2cos(A-B)=S^2+1

--->S^2=1+2cos(A-B)

-1=