已知tan²；a=2tan²；b+1，則cos2a+sin²；b=？過程越細越好

由tan²；a=2tan²；b+1得tan²；a+1=2tan²；b+1+1，即sec²；a=2sec²；bcos2a+sin²；b=2cos²；a-1+1-cos²；b=2cos²；a-cos²；b=2/sec²；a -1/sec²；b=2/（2sec²；b）-1/sec…