Line Curve Tangency
1. **State the problem:** Find values of $m$ for which the line $y=mx-6$ is tangent to the curve $y=x^2-4x+3$, and find the points of tangency.
2. **Set the line equal to the curve:** Since the line is tangent to the curve, they touch at exactly one point, so solve
$$mx - 6 = x^2 - 4x + 3.$$
Rearranging this,
$$x^2 - 4x - mx + 3 + 6 = 0$$
$$x^2 - (m+4)x + 9 = 0.$$
3. **Condition for tangency:** The quadratic equation must have exactly one solution, so its discriminant $ riangle$ must be zero.
$$ riangle = b^2 - 4ac = (-(m+4))^2 - 4(1)(9) = (m+4)^2 - 36 = 0.$$
4. **Solve for $m$:**
$$(m+4)^2 = 36$$
$$m+4 = \\pm 6.$$
Hence,
- Case 1: $m+4=6 \Rightarrow m=2$
- Case 2: $m+4=-6 \Rightarrow m=-10$
5. **Find points of tangency for each $m$:**
**Case $m=2$:** Solve
$$x^2 - (2+4)x + 9 = x^2 - 6x + 9 = 0.$$
This factors as
$$(x-3)^2=0,$$
so
$$x=3.$$
Calculate $y$:
$$y=mx-6=2(3)-6=6-6=0.$$
Point is $(3,0)$.
**Case $m=-10$:** Solve
$$x^2 - (-10+4)x + 9 = x^2 + 6x + 9 = 0.$$
This factors as
$$(x+3)^2=0,$$
so
$$x=-3.$$
Calculate $y$:
$$y = -10(-3) - 6 = 30 - 6 = 24.$$
Point is $(-3,24)$.
**Final answers:** The possible values of $m$ are $2$ and $-10$. The points of tangency are $(3,0)$ and $(-3,24)$, respectively.