12 multiple-choice questions, progressively harder.
Vertex AAA lies on y=8y=8y=8. In triangle ABCABCABC,
The altitude line from AAA passes through (2,2)(2,2)(2,2). What is AAA?
Solution
Correct answer: A
The side BCBCBC has slope 1/21/21/2, so the altitude has slope −2-2−2. Through (2,2)(2,2)(2,2) it satisfies
At height 8,
This point is not on the line of BCBCBC, so it gives a nondegenerate triangle.
Where does the perpendicular bisector of the segment from (−3,−1)(-3,-1)(−3,−1) to (5,5)(5,5)(5,5) meet the line y=−2x+8y=-2x+8y=−2x+8?
Correct answer: C
The segment midpoint is (1,2)(1,2)(1,2) and its slope is 3/43/43/4, so the bisector is
Substitute the other line's height.
The point satisfies both equations.
Triangle ABCABCABC has
Where do its altitude lines from AAA and CCC meet?
Correct answer: B
The altitude from CCC is vertical because ABABAB is horizontal.
Side BCBCBC has slope −2-2−2, so the altitude from AAA is
Substitution gives y=3/2y=3/2y=3/2, so the intersection is (2,3/2)(2,3/2)(2,3/2).
A line has equation y=(k−2)x+4y=(k-2)x+4y=(k−2)x+4. It is perpendicular to the line through (0,0)(0,0)(0,0) and (3,6)(3,6)(3,6). What is kkk?
Correct answer: D
The line through the two points has slope 2. The required perpendicular slope is −1/2-1/2−1/2.
This choice gives two nonzero defined slopes with product −1-1−1.
Its median line from CCC is parallel to y=53x−4y=\frac53x-4y=35x−4. What is ttt?
The midpoint of ABABAB is the origin. The median has slope t/9t/9t/9 and intercept zero. Parallelism requires
Its intercept differs from −4-4−4, so the lines are distinct. The side ABABAB has slope 2/32/32/3, so CCC does not lie on ABABAB.
The perpendicular bisector of the segment from
to
is vertical. Which value of kkk and bisector equation follow?
A vertical perpendicular bisector requires a horizontal segment, so the endpoints have equal second coordinates.
The midpoint's first coordinate is 1, so the vertical bisector is
Consider the three lines.
Which statement is correct?
The first two slopes are −1/2-1/2−1/2, but their intercepts are 2 and 5/25/25/2, so they are distinct parallels. The third slope is 2.
It is perpendicular to each. The first two have no common point, so three-way concurrence is impossible.
In triangle ABCABCABC,
Find the foot of the altitude from AAA on the full line of BCBCBC.
Side BCBCBC has slope 1/21/21/2 and equation
The perpendicular through AAA is
At their intersection,
The point lies on BCBCBC, and the slopes multiply to −1-1−1.
A nonvertical line has slope 2. A segment has slope −1/2-1/2−1/2. Which extra fact is sufficient to establish that the line is the segment's perpendicular bisector?
The slopes already establish the perpendicular direction.
The remaining condition in the perpendicular-bisector definition is passage through the midpoint. An arbitrary point or endpoint does not supply that condition.
Two slanted lines have slopes whose product is −1-1−1. Rotate the first through 90∘90^\circ90∘ about a point on it. Which fact completes the converse proof that the original lines are perpendicular?
The quarter-turn changes a nonzero slope mmm to
This is the second line's slope. Equal slopes give coincidence or parallelism. The original line is perpendicular to its rotated image, and the perpendicular transversal theorem handles the parallel case.
Segment ABABAB has
Its perpendicular bisector has slope 1/21/21/2. What is aaa?
The segment must have slope −2-2−2. Its endpoints have different second coordinates. A vertical segment would have a horizontal perpendicular bisector, which is excluded by the given nonzero slope.
The resulting segment is slanted, and its perpendicular slope is indeed 1/21/21/2.
Where do the altitude line from BBB and the median line from CCC meet?
The midpoint of ABABAB is (2,−2)(2,-2)(2,−2), so the median from CCC is vertical.
Side ACACAC has slope 2, so the altitude from BBB has slope −1/2-1/2−1/2.
At first coordinate 2, the height is zero, giving (2,0)(2,0)(2,0).
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