College

Circle Q is centered at the origin with radius [tex]r[/tex]. Point [tex]P(x, y)[/tex] lies on circle Q.

Make a conjecture: How can you find an equation relating the radius to the coordinates of point P?

Check all that apply:

- Notice that [tex]\triangle QPS[/tex] forms a right triangle.
- Because [tex]\triangle QPS[/tex] is a right triangle, apply the Pythagorean theorem.

Using the Pythagorean theorem, the equation relating the radius to the coordinates of point P is:

[tex]x^2 + y^2 = r^2[/tex]

Answer :

Sure! Let's solve the problem step by step.

We have a circle, Circle Q, centered at the origin (0, 0), and a point P(x, y) that lies on this circle. We want to find an equation relating the radius of the circle to the coordinates of point P.

### Step 1: Understand the Circle's Equation

For any circle centered at the origin with radius [tex]\( r \)[/tex], the standard equation is given by:

[tex]\[ x^2 + y^2 = r^2 \][/tex]

This equation helps us express the relationship between the coordinates of any point on the circle and the circle's radius.

### Step 2: Consider Points on the Circle

Since point P(x, y) lies on the circle, its coordinates must satisfy the circle's equation. In other words, substituting the coordinates of point P into the equation should hold true:

[tex]\[ x^2 + y^2 = r^2 \][/tex]

### Step 3: Consider the Geometry of the Situation

The hint given suggests noticing that triangle APQS forms a right triangle. In a right triangle like this, if you imagine line segments from the origin at Q to P, and another horizontal line to the x-axis, it forms a right triangle with:

- One leg along the x-axis (length [tex]\( x \)[/tex])
- Another leg from the x-axis to P (length [tex]\( y \)[/tex])
- The hypotenuse being the radius of the circle (length [tex]\( r \)[/tex])

### Step 4: Apply the Pythagorean Theorem

Because we have a right triangle formed, we apply the Pythagorean theorem, which states:

[tex]\[ \text{(leg}_1)^2 + \text{(leg}_2)^2 = \text{(hypotenuse)}^2 \][/tex]

Plugging in the segments we have:

[tex]\[ x^2 + y^2 = r^2 \][/tex]

### Conclusion

So the equation [tex]\( x^2 + y^2 = r^2 \)[/tex] describes the relationship between the radius of the circle and the coordinates of any point (x, y) on the circle. This is consistent with what we expect for a circle centered at the origin.

Thus, any time you have a point on a circle centered at the origin, the sum of the squares of its coordinates will equal the square of the radius of the circle.