Question

If seco - tano = 4 then prove that cosO=8/17​

Answer 1

Answer:

http://fleurmarsella.weebly.com/uploads/2/3/1/1/23113184/pc_12_-_trig_review_-_solutions.pdf

Answer 2

solution

Sec²A-tan²A=1

=>(secA-tanA)(secA+tanA)=1

=>4(secA+tanA)=1

=>secA+tanA=1/4

now....

secA-tanA=4

secA+tanA=1/4

___________________

secA=17/8

=>cosA=1/secA=8/17

=>cosA=8/17 (proved)