cos7acos3a+sin7asin3a/sin3acos3a•(-2sinasin6a/cos4a=-4sina
2cos4a/sin6a •(-2sinasin6a/cos4a=-4sina
-4cos4asina/cos4a=-4sina
-4sina=-4sina
cos7acos3a+sin7asin3a/sin3acos3a•(-2sinasin6a/cos4a=-4sina
2cos4a/sin6a •(-2sinasin6a/cos4a=-4sina
-4cos4asina/cos4a=-4sina
-4sina=-4sina