We need to solve the inequality $\sqrt{(a-3)^2} \sin a - 3 < 0$.

AnalysisInequalitiesTrigonometryAbsolute ValueFunctionsSolution of Inequalities
2025/3/11

1. Problem Description

We need to solve the inequality (a3)2sina3<0\sqrt{(a-3)^2} \sin a - 3 < 0.

2. Solution Steps

First, we simplify the square root:
(a3)2=a3\sqrt{(a-3)^2} = |a-3|.
So the inequality becomes a3sina3<0|a-3| \sin a - 3 < 0, which can be rewritten as a3sina<3|a-3| \sin a < 3.
Now, we consider two cases:
Case 1: a3a \ge 3. In this case, a3=a3|a-3| = a-3, so the inequality becomes (a3)sina<3(a-3) \sin a < 3.
Case 2: a<3a < 3. In this case, a3=3a|a-3| = 3-a, so the inequality becomes (3a)sina<3(3-a) \sin a < 3.
Now, let us consider the expression a3sina|a-3|\sin a. Since 1sina1-1 \le \sin a \le 1, then
a3a3sinaa3-|a-3| \le |a-3|\sin a \le |a-3|.
So, if a33|a-3| \le 3, then a3sina3|a-3| \sin a \le 3.
We have a33|a-3| \le 3, which implies 3a33-3 \le a-3 \le 3.
Adding 3 to all parts of the inequality, we have 0a60 \le a \le 6.
If a=3a=3, then a3=0|a-3| = 0, so a3sina=0<3|a-3|\sin a = 0 < 3. Thus a=3a=3 is a solution.
If a=0a=0, then a3=3|a-3| = 3, and sina=sin0=0\sin a = \sin 0 = 0, so a3sina=0<3|a-3|\sin a = 0 < 3. Thus a=0a=0 is a solution.
If a=6a=6, then a3=3|a-3| = 3. sina=sin60.2794\sin a = \sin 6 \approx -0.2794, so a3sina=3sin60.838<3|a-3|\sin a = 3 \sin 6 \approx -0.838 < 3. Thus a=6a=6 is a solution.
If a>6a > 6, then a3=a3>3|a-3| = a-3 > 3. Also, we know that sina1\sin a \le 1, so a3sina|a-3| \sin a could be less than

3. If $a$ is close to $2\pi$, say $a = 2\pi \approx 6.28$, then $|a-3| = |6.28-3| = 3.28$. $\sin a = \sin 2\pi = 0$, so $|a-3|\sin a = 0 < 3$. However, as $a$ gets larger, it is difficult to determine whether the inequality holds in general.

Let's analyze when (a3)sina<3(a-3) \sin a < 3 and (3a)sina<3(3-a) \sin a < 3 are not satisfied. This occurs when a>3a>3 and sina>3a3\sin a > \frac{3}{a-3} or when a<3a<3 and sina>33a\sin a > \frac{3}{3-a}.
When sina<0\sin a < 0, we are guaranteed that the inequalities hold.
When sina=0\sin a = 0, the inequalities are satisfied for any aa.
Consider the original inequality a3sina<3|a-3| \sin a < 3.
This inequality is satisfied when sina<0\sin a < 0 or when a3<3sina|a-3| < \frac{3}{\sin a} when sina>0\sin a > 0.

3. Final Answer

0a60 \le a \le 6

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