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Question

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 :

The correct answer is
26

Domain Calculation for Function $f(x)$

The function is given by $f(x) = \frac{1}{\sqrt{10+3x-x^2}} + \frac{1}{\sqrt{x+|x|}}$. To find the domain $(a, b)$, we need to consider the conditions under which each term is defined.

First Term Domain: $\frac{1}{\sqrt{10+3x-x^2}}$

  • For the square root in the denominator to be defined and non-zero, the expression inside must be strictly positive: $10+3x-x^2 > 0$.
  • Rewrite as: $x^2 - 3x - 10 < 0$.
  • Factor the quadratic: $(x-5)(x+2) < 0$.
  • This inequality holds true when $x$ is between the roots -2 and 5.
  • So, the domain for the first term is $-2 < x < 5$.

Second Term Domain: $\frac{1}{\sqrt{x+|x|}}$

  • The expression inside the square root must be strictly positive: $x+|x| > 0$.
  • Consider cases for $|x|$:
    • If $x > 0$, then $|x| = x$. The inequality becomes $x+x > 0 \implies 2x > 0 \implies x > 0$.
    • If $x \leq 0$, then $|x| = -x$. The inequality becomes $x+(-x) > 0 \implies 0 > 0$, which is false.
  • Therefore, the domain for the second term is $x > 0$.

Combined Domain $(a, b)$

The domain of the function $f(x)$ is the intersection of the domains of both terms.

  • Condition 1: $-2 < x < 5$
  • Condition 2: $x > 0$
  • The intersection is $0 < x < 5$.

Thus, the domain is $(a, b) = (0, 5)$. This implies $a=0$ and $b=5$.

Calculation of $(1+a)^2+b^2$

Substitute the values of $a$ and $b$ into the expression:

  • $(1+a)^2+b^2 = (1+0)^2 + 5^2$
  • $= 1^2 + 25$
  • $= 1 + 25$
  • $= 26$

The value of the expression is 26.

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