Answer to Question #128122 in Trigonometry for Tony

Question #128122
Prove that the inequality | cos(x)| ≥ 1 − sin2(x) holds true for all x ∈ R.
1
Expert's answer
2020-08-03T18:16:42-0400

Removing the mode;

cos x ≤ - (1 - sin²x) and cos x ≥ (1 - sin²x)


Considering;

cos x ≤ - (1 - sin²x)

cos x ≤ - 1 + sin²x

cos x - sin²x + 1 ≤ 0

cos x - (1 - cos²x) + 1 ≤ 0

cos x + cos²x ≤ 0

-1 ≤ cos x ≤ 0


True for all x ∈ R  and π/2+2πn ≤ x ≤ 3π/2+2πn .......(i)


Considering;

cos x ≥  (1 - sin²x)

cos x ≥  1 - sin²x

cos x + sin²x - 1 ≥ 0

cos x + (1 - cos²x) - 1 ≥ 0

cos x - cos²x + 1 ≥ 1

0 ≤ cos x ≤ 1


Therefore for all x ∈ R  and -π/2+2πn ≤ x ≤ π/2+2πn .......(ii)


combining equations (i) and (ii) we get,

For all x ∈ R  and -π/2+2πn ≤ x ≤ 3π/2+2πn.


Need a fast expert's response?

Submit order

and get a quick answer at the best price

for any assignment or question with DETAILED EXPLANATIONS!

Comments

Assignment Expert
06.10.20, 20:38

A solution of the inequality |A|>=B is equivalent to the union of solutions of two inequalities, namely A>=B, A

Rachel
06.10.20, 12:33

Please can you explain how to remove the mod

Leave a comment

LATEST TUTORIALS
New on Blog
APPROVED BY CLIENTS