Tangent Line Circle E7D889
1. **State the problem:** Find the equation of the tangent line to the circle given by $$x^2 + y^2 + 14x + 18y - 39 = 0$$ at the point in the second quadrant where $$x = -2$$.
2. **Rewrite the circle equation in standard form:** Complete the square for both $$x$$ and $$y$$.
$$x^2 + 14x + y^2 + 18y = 39$$
For $$x$$:
$$x^2 + 14x = (x + 7)^2 - 49$$
For $$y$$:
$$y^2 + 18y = (y + 9)^2 - 81$$
Substitute back:
$$ (x + 7)^2 - 49 + (y + 9)^2 - 81 = 39 $$
Simplify:
$$ (x + 7)^2 + (y + 9)^2 = 39 + 49 + 81 = 169 $$
So the circle has center $$C(-7, -9)$$ and radius $$r = \sqrt{169} = 13$$.
3. **Find the point on the circle where $$x = -2$$ in the second quadrant:**
Substitute $$x = -2$$ into the circle equation:
$$ (-2 + 7)^2 + (y + 9)^2 = 169 $$
Calculate:
$$ 5^2 + (y + 9)^2 = 169 $$
$$ 25 + (y + 9)^2 = 169 $$
$$ (y + 9)^2 = 144 $$
So:
$$ y + 9 = \pm 12 $$
Two possible $$y$$ values:
- $$y = 3$$
- $$y = -21$$
Since the point is in the second quadrant where $$x < 0$$ and $$y > 0$$, choose $$y = 3$$.
So the point of tangency is $$P(-2, 3)$$.
4. **Find the slope of the radius from center to point:**
$$ m_{radius} = \frac{3 - (-9)}{-2 - (-7)} = \frac{12}{5} $$
5. **Find the slope of the tangent line:**
The tangent line is perpendicular to the radius, so its slope is the negative reciprocal:
$$ m_{tangent} = -\frac{5}{12} $$
6. **Write the equation of the tangent line using point-slope form:**
$$ y - 3 = -\frac{5}{12}(x + 2) $$
Multiply both sides by 12 to clear denominator:
$$ 12(y - 3) = -5(x + 2) $$
Simplify:
$$ 12y - 36 = -5x - 10 $$
Bring all terms to one side:
$$ 5x + 12y - 26 = 0 $$
7. **Final answer:**
The equation of the tangent line is $$\boxed{5x + 12y - 26 = 0}$$, which corresponds to option c.