Math Problem Statement

Triangle PQR is rotated 90 degrees counterclockwise around the origin to form P'Q'R'. The triangle P'Q'R' is reflected across the x-axis to form P''Q''R''.

1

(a)

What are the signs of the coordinates of (x, y) of point P'? (Rotate point P 90 degrees counterclockwise to find your answer.)

A

Both x and y are positive 

B

x is negative, y is positive

C

x is positive, y is negative

D

Both x and y are negative

Solution

To determine the signs of the coordinates of point PP', we need to follow the transformation described:

Step 1: Understand the 90-degree counterclockwise rotation.

When a point (x,y)(x, y) is rotated 90 degrees counterclockwise around the origin, its new coordinates (x,y)(x', y') are given by: (x,y)=(y,x)(x', y') = (-y, x) This means:

  • The x-coordinate of the new point PP' will be the negative of the y-coordinate of the original point PP.
  • The y-coordinate of the new point PP' will be the x-coordinate of the original point PP.

Step 2: Analyze the signs of the coordinates after rotation.

Let's consider each quadrant and how the signs change:

  • If the original point PP is in Quadrant I (where both coordinates are positive), after rotation, PP' will be in Quadrant II, where the x-coordinate is negative and the y-coordinate is positive.
  • If PP is in Quadrant II (x is negative, y is positive), after rotation, PP' will be in Quadrant III (both x and y are negative).
  • If PP is in Quadrant III (both x and y are negative), after rotation, PP' will be in Quadrant IV (x is positive, y is negative).
  • If PP is in Quadrant IV (x is positive, y is negative), after rotation, PP' will be in Quadrant I (both x and y are positive).

Since we don’t have the exact coordinates of PP, the signs of PP''s coordinates depend on which quadrant PP is originally located in. But we can conclude from the general rule that a 90-degree counterclockwise rotation changes the signs in this way:

  • If PP is in Quadrant I, then after the rotation, x is negative and y is positive.

Thus, the answer is B: x is negative, y is positive.


Do you need more details or have any questions?

Here are 5 related questions you might consider:

  1. How does rotating a point by 180 degrees affect its coordinates?
  2. What are the coordinates of a point after a 270-degree counterclockwise rotation?
  3. How does reflection across the x-axis change a point's coordinates?
  4. What are the coordinates of a point after a reflection across the y-axis?
  5. How would you find the coordinates of PP'' after both a 90-degree rotation and reflection?

Tip: Always keep track of the quadrant your point moves to when applying transformations like rotations or reflections to easily determine sign changes.

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Math Problem Analysis

Mathematical Concepts

Geometry
Transformations
Coordinate Geometry

Formulas

(x', y') = (-y, x) for 90-degree counterclockwise rotation
Reflection across x-axis: (x, y) -> (x, -y)

Theorems

Rotation theorem
Reflection theorem

Suitable Grade Level

Grades 8-10