Integrals Y Squared
1. **Problem Statement:** Evaluate the integrals:
(a) $\int (y^2 + y^{-2})\, dy$
(b) $\int_1^2 (y^2 + y^{-2})\, dy$
(c) $\int_{-1}^2 (y^2 + y^{-2})\, dy$
2. **Step (a): Indefinite integral**
Write the integral:
$$\int (y^2 + y^{-2})\, dy = \int y^2\, dy + \int y^{-2}\, dy$$
For each term, use the power rule for integration:
$$\int y^n\, dy = \frac{y^{n+1}}{n+1} + C \quad \text{for } n \neq -1$$
Apply to each:
$$\int y^2\, dy = \frac{y^{3}}{3} + C$$
$$\int y^{-2}\, dy = \frac{y^{-1}}{-1} + C = -\frac{1}{y} + C$$
Combine:
$$\int (y^2 + y^{-2})\, dy = \frac{y^{3}}{3} - \frac{1}{y} + C$$
3. **Step (b): Definite integral from 1 to 2**
Evaluate:
$$\int_1^2 (y^2 + y^{-2})\, dy = \left[ \frac{y^3}{3} - \frac{1}{y} \right]_1^2 = \left( \frac{2^3}{3} - \frac{1}{2} \right) - \left( \frac{1^3}{3} - 1 \right)$$
Calculate each term:
$$\frac{2^3}{3} = \frac{8}{3}, \quad -\frac{1}{2} = -0.5$$
$$\frac{1^3}{3} = \frac{1}{3}, \quad -1 = -1$$
Substitute:
$$\left( \frac{8}{3} - \frac{1}{2} \right) - \left( \frac{1}{3} - 1 \right) = \left( \frac{8}{3} - 0.5 \right) - \left( \frac{1}{3} - 1 \right)$$
Calculate inside each parenthesis:
$$\frac{8}{3} - 0.5 = \frac{8}{3} - \frac{1}{2} = \frac{16}{6} - \frac{3}{6} = \frac{13}{6}$$
$$\frac{1}{3} - 1 = \frac{1}{3} - \frac{3}{3} = -\frac{2}{3}$$
So the expression becomes:
$$\frac{13}{6} - \left(-\frac{2}{3}\right) = \frac{13}{6} + \frac{2}{3} = \frac{13}{6} + \frac{4}{6} = \frac{17}{6}$$
Thus, the value is $\frac{17}{6}$.
4. **Step (c): Definite integral from -1 to 2**
The integrand $y^{-2} = \frac{1}{y^2}$ is not defined at $y=0$, so the integral is improper with a vertical asymptote at 0.
We split the integral at 0:
$$\int_{-1}^2 (y^2 + y^{-2})\, dy = \int_{-1}^0 (y^2 + y^{-2})\, dy + \int_0^2 (y^2 + y^{-2})\, dy$$
The term $\int y^{-2} dy$ diverges near 0 since $\lim_{y \to 0} -1/y$ goes to infinity.
Hence, the integral does not converge (it diverges) due to the discontinuity at 0.
**Final result:** The integral is divergent and thus undefined.
**Summary:**
(a) $\int (y^2 + y^{-2})\, dy = \frac{y^3}{3} - \frac{1}{y} + C$
(b) $\int_1^2 (y^2 + y^{-2})\, dy = \frac{17}{6}$
(c) $\int_{-1}^2 (y^2 + y^{-2})\, dy$ diverges and is undefined.