Question

Which shows all the exact solutions of 2sec^2 (x)-tan^4 (x)=-1? Give your answer in radians.

a) pi/3 + kpi and 2pi/3 + kpi
b) pi/3 +2kpi and 5pi/3 +2kpi
c) pi/4 +2kpi, 3pi/4 + 2kpi, 5pi/4 +2kpi, and 7pi/4 +2kpi
d) pi/3 + kpi, 2pi/3 +kpi, 4pi/3 +kpi, and 5pi/3 +kpi

Answer 1

a. 1/3pi+kpi and 2/3pi+kpi

Explanation:

2Sec²x

=2+2tan²x-(tan²x)²=-1

Let tan²x=u

-u²+2u+2=-1

-u²+2u+3=0

u²-2u-3=0

(u+1)(u-3)=0

u=-1,u=3

(tan x)²=-1(No solution)

(tan x)²=3

>>tan x=±sqrt(3)

I) tan x=sqrt(3)

>>tan(pi/3)=sqrt 3

Tan(pi+A) =tanA

Tan(pi+pi/3)=tan(pi/3)

>>tan(4/3pi)=sqrt(3)

>>x=4/3pi and 1/3pi

General solution: 1/3pi+kpi

ii) tan x=-sqrt(3)

x=2/3pi(At 2nd quadrant)

x=5/3pi(at 4th quadrant)

General solution: 2/3pi+kpi