JEE MAIN - Mathematics (2023 - 15th April Morning Shift - No. 5)
$f(x)=\log _{e}\left(4 x^{2}+11 x+6\right)+\sin ^{-1}(4 x+3)+\cos ^{-1}\left(\frac{10 x+6}{3}\right)$ is $(\alpha, \beta]$, then
$36|\alpha+\beta|$ is equal to :
Explanation
To find the domain of the function, we need to consider the individual functions and their respective domains. We have:
- $f_1(x) = \ln(4x^2 + 11x + 6)$
- $f_2(x) = \sin^{-1}(4x + 3)$
- $f_3(x) = \cos^{-1}\left(\frac{10x + 6}{3}\right)$
- For $f_1(x)$:
$$ 4x^2 + 11x + 6 > 0 $$
Factoring the quadratic expression:
$$ (4x + 3)(x + 2) > 0 $$
From this inequality, we have:
$$ x \in (-\infty, -2) \cup \left(-\frac{3}{4}, \infty\right) $$
- For $f_2(x)$:
$$ -1 \le 4x + 3 \le 1 $$
From these inequalities, we get:
$$ x \in \left[-1, -\frac{1}{2}\right] $$
- For $f_3(x)$:
$$ -1 \le \frac{10x + 6}{3} \le 1 $$
From these inequalities, we get:
$$ x \in \left[-\frac{9}{10}, -\frac{3}{10}\right] $$
Now, we need to find the intersection of the domains of the three functions:
$$ \left(-\infty, -2\right) \cup \left(-\frac{3}{4}, \infty\right) \cap \left[-1, -\frac{1}{2}\right] \cap \left[-\frac{9}{10}, -\frac{3}{10}\right] $$
To find the intersection, let's analyze the intervals:
- The interval $(-\infty, -2) \cup \left(-\frac{3}{4}, \infty\right)$ contains all $x$ values less than $-2$ and greater than $-\frac{3}{4}$.
- The interval $\left[-1, -\frac{1}{2}\right]$ contains all $x$ values between $-1$ and $-\frac{1}{2}$.
- The interval $\left[-\frac{9}{10}, -\frac{3}{10}\right]$ contains all $x$ values between $-\frac{9}{10}$ and $-\frac{3}{10}$.
Looking at the intervals, we can see that the intersection is:
$$ x \in \left(-\frac{3}{4}, -\frac{1}{2}\right] $$
Thus, the domain of the function is $(\alpha, \beta] = \left(-\frac{3}{4}, -\frac{1}{2}\right]$. Now, we need to find the value of $36|\alpha + \beta|$:
$$ 36\left|-\frac{3}{4} - \frac{1}{2}\right| = 36\left|-\frac{5}{4}\right| =45 $$
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