1. **State the problem:** Solve the equation $$a^3 + a^2 = 36$$ for the variable $a$.
2. **Rewrite the equation:** We want to find $a$ such that $$a^3 + a^2 - 36 = 0$$.
3. **Factor the equation if possible:** Factor out the common term $a^2$ from the first two terms:
$$a^2(a + 1) - 36 = 0$$
4. **Isolate terms:** Rewrite as
$$a^2(a + 1) = 36$$
5. **Try possible integer roots:** Since 36 is a perfect square and cube, test integer values for $a$.
6. **Test $a=3$:**
$$3^3 + 3^2 = 27 + 9 = 36$$ which satisfies the equation.
7. **Check for other roots:** The equation is cubic, so there may be other roots. Use the original form:
$$a^3 + a^2 - 36 = 0$$
8. **Use polynomial division to factor out $(a-3)$:**
Divide $$a^3 + a^2 - 36$$ by $(a-3)$:
$$\frac{a^3 + a^2 - 36}{a - 3} = a^2 + 4a + 12$$
9. **Solve quadratic $a^2 + 4a + 12 = 0$:**
Use quadratic formula:
$$a = \frac{-4 \pm \sqrt{4^2 - 4 \times 1 \times 12}}{2} = \frac{-4 \pm \sqrt{16 - 48}}{2} = \frac{-4 \pm \sqrt{-32}}{2}$$
10. **Simplify the discriminant:**
$$\sqrt{-32} = \sqrt{32}i = 4\sqrt{2}i$$
11. **Final roots from quadratic:**
$$a = \frac{-4 \pm 4\sqrt{2}i}{2} = -2 \pm 2\sqrt{2}i$$
12. **Summary of solutions:**
- Real root: $$a = 3$$
- Complex roots: $$a = -2 + 2\sqrt{2}i$$ and $$a = -2 - 2\sqrt{2}i$$
**Final answer:** $$\boxed{a = 3, \quad a = -2 \pm 2\sqrt{2}i}$$
Solve Cubic 800Cb9
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