1. **Problem statement:** Find the values of $a$ and $b$ for the cubic curve $$y = x^3 + ax^2 + bx + 3$$ given that it passes through the point $(1,8)$ and the tangent line at that point is $$y = 2x + 6.$$
2. **Step 1: Use the point on the curve.** Substitute $x=1$ and $y=8$ into the cubic equation:
$$8 = 1^3 + a(1)^2 + b(1) + 3 = 1 + a + b + 3 = a + b + 4.$$
Simplify to get:
$$a + b = 4.$$
3. **Step 2: Use the slope of the tangent line.** The derivative of the cubic curve is:
$$y' = 3x^2 + 2ax + b.$$
At $x=1$, the slope of the tangent line is given by the derivative:
$$y'(1) = 3(1)^2 + 2a(1) + b = 3 + 2a + b.$$
The slope of the tangent line $y = 2x + 6$ is 2, so:
$$3 + 2a + b = 2.$$
Simplify:
$$2a + b = 2 - 3 = -1.$$
4. **Step 3: Solve the system of equations:**
From step 2 and 3, we have:
$$\begin{cases} a + b = 4 \\ 2a + b = -1 \end{cases}$$
Subtract the first equation from the second:
$$\cancel{2a} + b - (\cancel{a} + b) = -1 - 4$$
$$a = -5.$$
Substitute $a = -5$ into $a + b = 4$:
$$-5 + b = 4 \implies b = 9.$$
5. **Final answer:**
$$a = -5, \quad b = 9.$$
Cubic Curve Tangent 9Bdf1E
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