Question Details

If tan4θ+tan2θ=1, what is the value of 11(cos4θ+cos2θ)?

Options

A

−11

B

8

C

0

D

11

Show Answer

Correct Answer :

Option D

11

11

Solution :

To find the value of the expression 11(cos4θ+cos2θ), we start with the given trigonometric equation:
tan4θ+tan2θ=1

We can factor out tan2θ from the left side of the equation:
tan2θ(tan2θ+1)=1

Using the fundamental trigonometric identity 1+tan2θ=sec2θ, we can substitute this into the equation:
tan2θsec2θ=1

Next, we express tanθ and secθ in terms of sinθ and cosθ:
tanθ=sinθcosθ and secθ=1cosθ

Substituting these definitions, the equation becomes:
sin2θcos2θ1cos2θ=1
sin2θcos4θ=1
Multiplying both sides by cos4θ, we obtain:
sin2θ=cos4θ

Now, we substitute this relation into the expression we want to evaluate: cos4θ+cos2θ.
Replacing cos4θ with sin2θ:
cos4θ+cos2θ=sin2θ+cos2θ

By the standard Pythagorean trigonometric identity, we know that:
sin2θ+cos2θ=1
Therefore, we have:
cos4θ+cos2θ=1

Finally, we multiply this value by 11:
11(cos4θ+cos2θ)=11(1)=11

Thus, the correct option is 11.

Unlock Our Free Library

Access expert-curated educational resources and study materials—completely free.

Ask AI Tutor
5 left
Q1 View Question & Options
AI Tutor is solving this question...
Reading question context & options...