Subjects algebra

Solve Cubic 92488B

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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. **Test $a=-4$:** $$(-4)^3 + (-4)^2 = -64 + 16 = -48 eq 36$$ 8. **Check for other roots:** The equation is cubic, so there may be other roots. Use the Rational Root Theorem or numerical methods. 9. **Use substitution or numerical methods:** Since $a=3$ works, divide the cubic polynomial by $(a-3)$: $$a^3 + a^2 - 36 = (a - 3)(a^2 + 4a + 12)$$ 10. **Solve quadratic:** $$a^2 + 4a + 12 = 0$$ Use quadratic formula: $$a = \frac{-4 \pm \sqrt{4^2 - 4 \times 1 \times 12}}{2} = \frac{-4 \pm \sqrt{16 - 48}}{2} = \frac{-4 \pm \sqrt{-32}}{2}$$ 11. **Simplify roots:** $$a = \frac{-4 \pm 4i\sqrt{2}}{2} = -2 \pm 2i\sqrt{2}$$ 12. **Final solutions:** - Real root: $$a = 3$$ - Complex roots: $$a = -2 + 2i\sqrt{2}$$ and $$a = -2 - 2i\sqrt{2}$$ **Answer:** The real solution is $$\boxed{3}$$.