1. **State the problem:**
We have a continuous random variable $X$ with probability density function (pdf) $$f(x) = k(2 - x)(2 + x), \quad 0 \leq x \leq 2.$$ We need to find:
(i) The value of constant $k$.
(ii) $P(X=2)$.
(iii) $P(X \leq 1)$.
(iv) $P(X \geq 1)$.
(v) $P(0.5 \leq X \leq 1.5)$.
2. **Find $k$ using the property of pdf:**
The total probability must be 1, so
$$\int_0^2 f(x) \, dx = 1.$$
Substitute $f(x)$:
$$\int_0^2 k(2 - x)(2 + x) \, dx = 1.$$
Expand the product:
$$(2 - x)(2 + x) = 4 - x^2,$$
so
$$k \int_0^2 (4 - x^2) \, dx = 1.$$
Calculate the integral:
$$k \left[4x - \frac{x^3}{3}\right]_0^2 = 1.$$
Evaluate at limits:
$$k \left(4 \times 2 - \frac{2^3}{3} - 0\right) = 1,$$
$$k \left(8 - \frac{8}{3}\right) = 1,$$
$$k \times \frac{24 - 8}{3} = 1,$$
$$k \times \frac{16}{3} = 1,$$
Divide both sides by $\frac{16}{3}$:
$$k = \frac{1}{\frac{16}{3}} = \frac{3}{16}.$$
3. **Calculate $P(X=2)$:**
For continuous variables, $P(X = a) = 0$ for any $a$, so
$$P(X=2) = 0.$$
4. **Calculate $P(X \leq 1)$:**
$$P(X \leq 1) = \int_0^1 f(x) \, dx = \int_0^1 \frac{3}{16}(4 - x^2) \, dx.$$
Calculate the integral:
$$\frac{3}{16} \left[4x - \frac{x^3}{3}\right]_0^1 = \frac{3}{16} \left(4 \times 1 - \frac{1}{3}\right) = \frac{3}{16} \times \frac{12 - 1}{3} = \frac{3}{16} \times \frac{11}{3} = \frac{11}{16}.$$
5. **Calculate $P(X \geq 1)$:**
Since total probability is 1,
$$P(X \geq 1) = 1 - P(X < 1) = 1 - P(X \leq 1) = 1 - \frac{11}{16} = \frac{5}{16}.$$
6. **Calculate $P(0.5 \leq X \leq 1.5)$:**
$$P(0.5 \leq X \leq 1.5) = \int_{0.5}^{1.5} \frac{3}{16}(4 - x^2) \, dx = \frac{3}{16} \left[4x - \frac{x^3}{3}\right]_{0.5}^{1.5}.$$
Evaluate at limits:
At $x=1.5$:
$$4 \times 1.5 - \frac{(1.5)^3}{3} = 6 - \frac{3.375}{3} = 6 - 1.125 = 4.875,$$
At $x=0.5$:
$$4 \times 0.5 - \frac{(0.5)^3}{3} = 2 - \frac{0.125}{3} = 2 - 0.0416667 = 1.9583333,$$
Subtract:
$$4.875 - 1.9583333 = 2.9166667,$$
Multiply by $\frac{3}{16}$:
$$\frac{3}{16} \times 2.9166667 = 0.546875 = \frac{35}{64}.$$
**Final answers:**
(i) $k = \frac{3}{16}$
(ii) $P(X=2) = 0$
(iii) $P(X \leq 1) = \frac{11}{16}$
(iv) $P(X \geq 1) = \frac{5}{16}$
(v) $P(0.5 \leq X \leq 1.5) = \frac{35}{64}$
Pdf Probabilities D339Be
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