1-cosx/1+cosx=secx-1/secx+1 Verify the identity. I tried all identities that I could, but could not find how it worked. Can you show me how to verify with all steps?

Dakota earned $7.50 in interest in account a and $18.75 in interest in account b after 15 months. if the simple interest rate is 4% for account a and 5% for account b, which account has the greater principal? explain. to make it a little easier, there is an image. good luck!