Solve Trigonometric Inequality 5x≤8sinx−sin2x≤6x

In summary, a trigonometric inequality is an inequality involving trigonometric functions, typically solved for a range of values. To solve one, isolate the trigonometric function, use algebraic techniques, and graph the solution set. The main difference between solving an equation and an inequality is that an equation has a single solution while an inequality has a range of solutions. A calculator can be used, but it's important to understand the steps involved. Common mistakes include not considering the period, not isolating the function, and not checking for extraneous solutions.
  • #1
lfdahl
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$5x \le 8\sin x - \sin 2x \le 6x$ for $0 \le x \le \frac{\pi}{3}$.
 
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  • #2
Hint:

If $f(x) = 8\sin x - \sin 2x$, show that $5 \le f'(x) \le 6$ on $[0;\frac{\pi}{3}]$.
 
  • #3
Suggested solution:
Let
\[f(x) = 8 \sin x - \sin 2x \\\\ f'(x) = 8 \cos x - 2 \cos 2x \\\\ f''(x) = -8 \sin x +4 \sin 2x = -8 \sin x(1- \cos x)\]

From these we see $f'(0) = 6, f'(\pi/3) = 5, f(0) = 0$ and $f''(x) \leq 0$ on $[0;\pi/3].$

Hence, $5\leq f'(x) \leq 6$ on $[0;\pi/3].$

Integrating from $0$ to $x$ gives

\[5x \leq f(x) \leq 6x.\]
 

FAQ: Solve Trigonometric Inequality 5x≤8sinx−sin2x≤6x

What is a trigonometric inequality?

A trigonometric inequality is an inequality that involves trigonometric functions, such as sine, cosine, and tangent. These inequalities are typically solved for a range of values of the variable, rather than a single solution.

How do I solve a trigonometric inequality?

To solve a trigonometric inequality, you must first isolate the trigonometric function on one side of the inequality. Then, use algebraic techniques, such as factoring and the quadratic formula, to solve for the variable. Finally, graph the solution set to determine the range of values that satisfy the inequality.

What is the difference between solving a trigonometric equation and a trigonometric inequality?

A trigonometric equation has a single solution, while a trigonometric inequality has a range of solutions. Additionally, solving a trigonometric inequality may involve using algebraic techniques, while solving a trigonometric equation typically only requires finding the inverse of the trigonometric function.

Can I use a calculator to solve a trigonometric inequality?

Yes, you can use a calculator to help solve a trigonometric inequality. However, it is important to understand the steps involved in solving the inequality by hand before relying on a calculator.

What are some common mistakes when solving trigonometric inequalities?

Some common mistakes when solving trigonometric inequalities include forgetting to consider the period of the trigonometric function, not isolating the function on one side of the inequality, and not graphing the solution set to check for extraneous solutions. It is important to carefully follow each step and check your work to avoid these mistakes.

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