Let the equations of two adjacent sides of a parallelogram ABCD be and . \text{If the equation of its one diagonal AC is \text{ and the distance of A from the other diagonal is , then is equal to:
- A
- B
- C
- D
Let the equations of two adjacent sides of a parallelogram ABCD be and . \text{If the equation of its one diagonal AC is \text{ and the distance of A from the other diagonal is , then is equal to:
Correct answer:A
Standard Method
Given: The adjacent sides are and , and one diagonal is .
Find: The value of , where is the distance of point from the other diagonal.
First, find the vertex as the intersection of the two given side lines:
Solving gives .
Using the diagonal , the other endpoint is obtained as .
Now find the midpoint of diagonal :
The diagonals of a parallelogram bisect each other, so diagonal also passes through . Using the line through the points and , the equation of diagonal is obtained as:
Now use the distance formula from point to the line :
Therefore,
So, the correct option is A.
Finding the distance from point to the diagonal instead of the other diagonal . This is wrong because the question explicitly asks for the distance from to the other diagonal. First determine the equation of , then apply the point-to-line distance formula.
Using an incorrect midpoint property for a parallelogram. The diagonals bisect each other, so the midpoint of and must be the same. If this is missed, the equation of will be wrong.
Substituting into the distance formula without taking the absolute value in the numerator. The distance from a point to a line is always non-negative, so use .
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