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Evaluate the integral and express your answer in simplest form.

int(-2)/(9+25x^(2))dx
Answer:

Evaluate the integral and express your answer in simplest form.\newline29+25x2dx \int \frac{-2}{9+25 x^{2}} d x \newlineAnswer:

Full solution

Q. Evaluate the integral and express your answer in simplest form.\newline29+25x2dx \int \frac{-2}{9+25 x^{2}} d x \newlineAnswer:
  1. Recognize Integral Form: We are given the integral to evaluate: \newline29+25x2dx\int \frac{-2}{9+25x^{2}}\,dx\newlineFirst, we notice that the denominator can be written as a sum of squares, which suggests a trigonometric substitution. However, we can also use a direct substitution if we recognize that the integral is in the form of an arctangent function. We will use the substitution method.
  2. Substitution with u: Let's make the substitution u=5xu = 5x, which means du=5dxdu = 5dx. We need to express dxdx in terms of dudu, so we get dx=du5dx = \frac{du}{5}.
  3. Factor Out Constants: Now we substitute 5x5x with uu and dxdx with du/5du/5 in the integral:\newline29+25x2dx=29+u2(du5)\int\frac{-2}{9+25x^{2}}dx = \int\frac{-2}{9+u^{2}} \cdot \left(\frac{du}{5}\right)\newlineWe can factor out constants from the integral:\newline=(25)19+u2du= \left(-\frac{2}{5}\right) \cdot \int\frac{1}{9+u^{2}}du
  4. Use Integral Formula: The integral of 1a2+u2\frac{1}{a^2 + u^2} is 1aarctan(ua)+C\frac{1}{a} \cdot \arctan\left(\frac{u}{a}\right) + C, where aa is a constant. In our case, a2=9a^2 = 9, so a=3a = 3. We can now integrate using this formula:\newline(25)19+u2du=(25)(13)arctan(u3)+C\left(-\frac{2}{5}\right) \cdot \int \frac{1}{9+u^{2}}du = \left(-\frac{2}{5}\right) \cdot \left(\frac{1}{3}\right) \cdot \arctan\left(\frac{u}{3}\right) + C
  5. Simplify Constant Factors: Simplify the constant factors:\newline(25)×(13)=215(-\frac{2}{5}) \times (\frac{1}{3}) = -\frac{2}{15}\newlineSo the integral becomes:\newline215×arctan(u3)+C-\frac{2}{15} \times \text{arctan}(\frac{u}{3}) + C
  6. Substitute Back u: Now we substitute back u=5xu = 5x to get the integral in terms of xx:215arctan(5x3)+C-\frac{2}{15} \cdot \arctan\left(\frac{5x}{3}\right) + C
  7. Final Indefinite Integral: We have found the indefinite integral in its simplest form: 29+25x2dx=215arctan(5x3)+C\int \frac{-2}{9+25x^{2}}dx = \frac{-2}{15} \cdot \arctan\left(\frac{5x}{3}\right) + C