# Circles HW #1.

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Circles HW #1

Complete the square and write as a squared binomial.
1. x2 + 6x + _____ = _____________ 2. x2 – 10x + _____ = _____________ 3. x2 + 24x + _____ = _____________ 4. x2 + 2x + _____ = _____________ 5. x2 – 5x + _____ = ______________ 6. This will be a critical skill we will use later on with conic sections!

Solve by completing the square:
x2 + 6x – 16 = 0 x2 – 4x = 11

Write the equation in standard form for the given circle:

Lines Tangent to Circles
Section: 5.2 (Green Book) Circles Quiz: Thursday Circles Test: Sept. 17

Chord: A line segment whose endpoints are on the circle Secant: A line that intersects the circle in two points Radius: The distance from the center to a point on the circle

Diameter: A chord that passes through the center of the circle Tangent: A line in the plane of a circle that intersects the circle in EXACTLY one point

Helpful Theorems If a line is tangent to a circle, then it is perpendicular to the radius drawn to the point of tangency

Helpful Theorems In a plane, if a line is perpendicular to a radius of a circle at its endpoint on the circle, then the line is tangent to the circle.

If two lines are Perpendicular…
What do we know about their slopes? Their slopes are opposite reciprocals to each other!!!!!!!! Let’s use this to find some tangents….

Find an equation of the line tangent to the given circle at the given point
What’s the slope of the radius to point (-1, 3)? So……..

Slope of Tangent The slope of the tangent must be the opposite reciprocal of -3, which is

Writing the Equation Point Slope Form:
So to write the equation of our tangent line:

OR You can use Slope-Intercept form:
y = 1/3x + b  plug in the point,(-1, 3) to find b

Find an equation of the line tangent to the given circle at the given point
(x – 3)2 + (y + 2)2 = 130 at point (-4, 7)

Write a circular model Cell Phones
A cellular phone tower services a 10 mile radius. You get a flat tire 4 miles east and 9 miles north of the tower. Are you in the tower’s range? SOLUTION In the diagram above, the origin represents the tower and the positive y-axis represents north. STEP 1 Write an inequality for the region covered by the tower. From the diagram, this region is all points that satisfy the following inequality: x2 + y2 < 102

Write a circular model continued….
STEP 2 Substitute the coordinates (4, 9) into the inequality from Step 1. x2 + y2 < 102 Inequality from Step 1 < 102 ? Substitute for x and y. 97 < 100 The inequality is true. ANSWER So, you are in the tower’s range.

HOMEWORK Circle Homework #2 WS