不接受通过精确作图得出的解。 点 A、B 和 C 的坐标分别为 、 和 。
- (i)
求三角形 的面积。
- (ii)
已知点 的坐标为 ,判断点 、 和 是否共线,并说明理由。
- (iii)
求从点 到直线 的垂足的坐标。
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完整解法
10(i)
1. Apply the shoelace formula to find the area of the triangle
2. Evaluate the determinant to find the final area
units
10(ii)
1. Calculate the gradient of the line segment AB
Gradient of
2. Calculate the gradient of the line segment AD
Gradient of
3. Compare the gradients to determine collinearity
Since the gradient of gradient of , the points , and do not lie on the same straight line. Therefore, they are not collinear.
Since the gradient of is not equal to the gradient of , the points , and are not collinear.
10(iii)
1. Find the gradient of the line $BC$.
Gradient of
2. Find the equation of the line $BC$.
3. Find the gradient and equation of the perpendicular line from $A$ to $BC$.
Gradient of perpendicular line
Equation of perpendicular line passing through :
4. Solve the equations simultaneously to find the coordinates of the foot of the perpendicular.
Substitute into :
Substitute into :
The coordinates of the foot of the perpendicular are .
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