Question

prove that sec²A + cos²A can never be less than 2

Answer 1

Let us put A=0°  So.... Sec²0°+cos²0°=infinite (or not defined)  Let's put it equal to 30°... So.... Sec²30+cos²30°=4/3+3/4=25/12≈2.08  Now....  For A=45° We get sec²45°+cos²45=2.5  So......for all values of A the sum will be always more than 2