Derivative Quotient 75B31F
1. **State the problem:** Find the derivative of the function $$y=\frac{2x^3 + x}{3x - 1}$$.
2. **Recall the formula:** For a function $$y=\frac{u}{v}$$, the derivative is given by the quotient rule:
$$y' = \frac{v u' - u v'}{v^2}$$
where $$u = 2x^3 + x$$ and $$v = 3x - 1$$.
3. **Calculate the derivatives of numerator and denominator:**
- $$u' = \frac{d}{dx}(2x^3 + x) = 6x^2 + 1$$
- $$v' = \frac{d}{dx}(3x - 1) = 3$$
4. **Apply the quotient rule:**
$$y' = \frac{(3x - 1)(6x^2 + 1) - (2x^3 + x)(3)}{(3x - 1)^2}$$
5. **Expand the numerator:**
- First term: $$(3x)(6x^2) = 18x^3$$
- $$(3x)(1) = 3x$$
- $$(-1)(6x^2) = -6x^2$$
- $$(-1)(1) = -1$$
So, $$(3x - 1)(6x^2 + 1) = 18x^3 + 3x - 6x^2 - 1$$
- Second term: $$(2x^3 + x)(3) = 6x^3 + 3x$$
6. **Subtract the second term from the first:**
$$18x^3 + 3x - 6x^2 - 1 - (6x^3 + 3x) = (18x^3 - 6x^3) + (3x - 3x) - 6x^2 - 1 = 12x^3 - 6x^2 - 1$$
7. **Write the final derivative:**
$$y' = \frac{12x^3 - 6x^2 - 1}{(3x - 1)^2}$$
**Note:** The derivative you proposed, $$\frac{12x^3 + 6x^2 -1}{(3x -1)^2}$$, has incorrect signs in the numerator. The correct signs are as shown above.