1.tan(a-b)=(tanA-tanB)/(1+tanA*tanB)=1/2
tanb=-1/7
带入,得tanA=1/3
tan(2a-b)=tan[a+(a-b)]=[tanA+tan(a-b)]/[1-tanA*tan(a-b)]=1
因为a,b都为一二象限,所以0
1.tan(a-b)=(tanA-tanB)/(1+tanA*tanB)=1/2
tanb=-1/7
带入,得tanA=1/3
tan(2a-b)=tan[a+(a-b)]=[tanA+tan(a-b)]/[1-tanA*tan(a-b)]=1
因为a,b都为一二象限,所以0