Question ID: #1015
If the domain of the function $f(x)=\frac{1}{\sqrt{10+3x-x^{2}}}+\frac{1}{\sqrt{x+|x|}}$ is $(a, b)$, then $(1+a)^{2}+b^{2}$ is equal to:
- (1) $26$
- (2) $29$
- (3) $25$
- (4) $30$
Solution:
For the function to be defined, the expressions inside the square roots in the denominator must be strictly positive.
$$10+3x-x^{2} > 0$$
$$x^{2}-3x-10 < 0$$
$$(x-5)(x+2) < 0$$
$$x \in (-2, 5)$$
$$x+|x| > 0$$
$$|x| > -x$$
This inequality holds true only for strictly positive real numbers.
$$x \in (0, \infty)$$
The domain of the function is the intersection of the intervals from both conditions:
$$x \in (-2, 5) \cap (0, \infty)$$
$$x \in (0, 5)$$
Comparing this with the given domain $(a, b)$:
$$a = 0, \quad b = 5$$
Calculate the required value:
$$(1+a)^{2} + b^{2} = (1+0)^{2} + (5)^{2}$$
$$(1+a)^{2} + b^{2} = 1 + 25 = 26$$
Ans. (1)
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