Line l passes through the points (-4, 4) and (8, -2).

  1. (a)

    Find the equation of line l.

    Answer ...

  2. (b)

    The equation of line m is 6y = 18 - 3x.
    Show how you can tell that the line m does not intersect the line l.

    Answer

  3. (c)

    The equation of line n is 2y=3x−42y = 3x - 4.

    Line n and line l intersect at point A. Find the coordinates of A.

    Answer A (..., ...)

  4. (d)

    Line l intersects the y-axis at point B and line n intersects the y-axis at point C.
    Calculate the area of triangle ABC.

    Answer ... units^2

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Worked solution

(a)

1. 计算直线 $l$ 的斜率

利用斜率公式 m=y2−y1x2−x1m = \dfrac{y_2 - y_1}{x_2 - x_1} 代入点 (−4,4)(-4, 4) 和 (8,−2)(8, -2):
m=−2−48−(−4)=−612=−12m = \frac{-2 - 4}{8 - (-4)} = \frac{-6}{12} = -\frac{1}{2}

2. 求直线 $l$ 的方程

代入点斜式 y−y1=m(x−x1)y - y_1 = m(x - x_1):
y−4=−12(x−(−4))y - 4 = -\frac{1}{2}(x - (-4))
y−4=−12x−2y - 4 = -\frac{1}{2}x - 2
y=−12x+2y = -\frac{1}{2}x + 2

Answer

y=−12x+2y = -\frac{1}{2}x + 2

(b)

1. 将直线 $m$ 的方程变形为斜截式

直线 mm 的方程为 6y=18−3x6y = 18 - 3x:
y=−36x+186y = -\frac{3}{6}x + \frac{18}{6}
y=−12x+3y = -\frac{1}{2}x + 3

2. 比较斜率和截距,给出不相交的理由

直线 mm 的斜率为 −12-\frac{1}{2},yy 轴截距为 33;
直线 ll 的斜率也为 −12-\frac{1}{2},yy 轴截距为 22。
因为两直线斜率相等且截距不同,所以直线 mm 与直线 ll 平行且不重合,故它们不相交。

Answer

直线 mm 的斜率与直线 ll 的斜率均为 −12-\frac{1}{2},且两直线的 yy 轴截距不同(分别为 33 和 22),故两直线平行且不重合,因此不相交。

(c)

1. 联立直线 $l$ 和直线 $n$ 的方程并消元

直线 ll: y=−12x+2  ⟹  2y=−x+4y = -\frac{1}{2}x + 2 \implies 2y = -x + 4
直线 nn: 2y=3x−42y = 3x - 4

将两式左边相等代入:
3x−4=−x+43x - 4 = -x + 4

2. 求解 $x$ 与 $y$ 的值

4x=8  ⟹  x=24x = 8 \implies x = 2

代入 y=−12(2)+2y = -\frac{1}{2}(2) + 2:
y=−1+2=1y = -1 + 2 = 1

因此交点 AA 的坐标为 (2,1)(2, 1)。

Answer

(2,1)(2, 1)

(d)

1. 求点 $B$ 和点 $C$ 的坐标

直线 ll: y=−12x+2y = -\frac{1}{2}x + 2,令 x=0x = 0,得 y=2y = 2,故 B(0,2)B(0, 2)。
直线 nn: 2y=3x−42y = 3x - 4,令 x=0x = 0,得 2y=−4  ⟹  y=−22y = -4 \implies y = -2,故 C(0,−2)C(0, -2)。

2. 计算三角形 $ABC$ 的底边和高并求面积

线段 BCBC 位于 yy 轴上,其长度作为底边:
底边 BC=2−(−2)=4\text{底边 } BC = 2 - (-2) = 4

顶点 A(2,1)A(2, 1) 到 yy 轴(线段 BCBC)的垂直距离作为高:
高 h=∣xA∣=2\text{高 } h = |x_A| = 2

因此,三角形 ABCABC 的面积为:
面积=12×BC×h=12×4×2=4\text{面积} = \frac{1}{2} \times BC \times h = \frac{1}{2} \times 4 \times 2 = 4

Answer

44

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