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Five-Minute Check (over Chapter 4) CCSS Then/Now New Vocabulary Theorems: Perpendicular Bisectors Example 1: Use the Perpendicular Bisector Theorems Theorem 5.3: Circumcenter Theorem Proof: Circumcenter Theorem Example 2: Real-World Example: Use the Circumcenter Theorem Theorems: Angle Bisectors Example 3: Use the Angle Bisector Theorems Theorem 5.6: Incenter Theorem Example 4: Use the Incenter Theorem Lesson Menu

Classify the triangle. A. scalene B. isosceles C. equilateral 5-Minute Check 1

Find x if mA = 10x + 15, mB = 8x – 18, and mC = 12x + 3. 5-Minute Check 2

Name the corresponding congruent sides if ΔRST  ΔUVW. A. R  V, S  W, T  U B. R  W, S  U, T  V C. R  U, S  V, T  W D. R  U, S  W, T  V 5-Minute Check 3

Name the corresponding congruent sides if ΔLMN  ΔOPQ. B. C. D. , 5-Minute Check 4

Find y if ΔDEF is an equilateral triangle and mF = 8y + 4. B. 10.75 C. 7 D. 4.5 5-Minute Check 5

ΔABC has vertices A(–5, 3) and B(4, 6) ΔABC has vertices A(–5, 3) and B(4, 6). What are the coordinates for point C if ΔABC is an isosceles triangle with vertex angle A? A. (–3, –6) B. (4, 0) C. (–2, 11) D. (4, –3) 5-Minute Check 6

G.CO.10 Prove theorems about triangles. Content Standards G.CO.10 Prove theorems about triangles. G.MG.3 Apply geometric methods to solve problems (e.g., designing an object or structure to satisfy physical constraints or minimize cost; working with typographic grid systems based on ratios). Mathematical Practices 1 Make sense of problems and persevere in solving them. 3 Construct viable arguments and critique the reasoning of others. CCSS

You used segment and angle bisectors. Identify and use perpendicular bisectors in triangles. Identify and use angle bisectors in triangles. Then/Now

perpendicular bisector concurrent lines point of concurrency circumcenter incenter Vocabulary

Concept

BC = AC Perpendicular Bisector Theorem BC = 8.5 Substitution Use the Perpendicular Bisector Theorems A. Find BC. BC = AC Perpendicular Bisector Theorem BC = 8.5 Substitution Answer: 8.5 Example 1

B. Find XY. Answer: 6 Use the Perpendicular Bisector Theorems Example 1

PQ = RQ Perpendicular Bisector Theorem 3x + 1 = 5x – 3 Substitution Use the Perpendicular Bisector Theorems C. Find PQ. PQ = RQ Perpendicular Bisector Theorem 3x + 1 = 5x – 3 Substitution 1 = 2x – 3 Subtract 3x from each side. 4 = 2x Add 3 to each side. 2 = x Divide each side by 2. So, PQ = 3(2) + 1 = 7. Answer: 7 Example 1

A. Find NO. A. 4.6 B. 9.2 C. 18.4 D. 36.8 Example 1

B. Find TU. A. 2 B. 4 C. 8 D. 16 Example 1

C. Find EH. A. 8 B. 12 C. 16 D. 20 Example 1

Concept

Concept

Use the Circumcenter Theorem GARDEN A triangular-shaped garden is shown. Can a fountain be placed at the circumcenter and still be inside the garden? By the Circumcenter Theorem, a point equidistant from three points is found by using the perpendicular bisectors of the triangle formed by those points. Example 2

Use the Circumcenter Theorem Copy ΔXYZ, and use a ruler and protractor to draw the perpendicular bisectors. The location for the fountain is C, the circumcenter of ΔXYZ, which lies in the exterior of the triangle. C Answer: No, the circumcenter of an obtuse triangle is in the exterior of the triangle. Example 2

BILLIARDS A triangle used to rack pool balls is shown BILLIARDS A triangle used to rack pool balls is shown. Would the circumcenter be found inside the triangle? A. No, the circumcenter of an acute triangle is found in the exterior of the triangle. B. Yes, circumcenter of an acute triangle is found in the interior of the triangle. Example 2

Concept

DB = DC Angle Bisector Theorem DB = 5 Substitution Use the Angle Bisector Theorems A. Find DB. DB = DC Angle Bisector Theorem DB = 5 Substitution Answer: DB = 5 Example 3

Use the Angle Bisector Theorems B. Find mWYZ. Example 3

WYZ  XYW Definition of angle bisector Use the Angle Bisector Theorems WYZ  XYW Definition of angle bisector mWYZ = mXYW Definition of congruent angles mWYZ = 28 Substitution Answer: mWYZ = 28 Example 3

QS = SR Angle Bisector Theorem 4x – 1 = 3x + 2 Substitution Use the Angle Bisector Theorems C. Find QS. QS = SR Angle Bisector Theorem 4x – 1 = 3x + 2 Substitution x – 1 = 2 Subtract 3x from each side. x = 3 Add 1 to each side. Answer: So, QS = 4(3) – 1 or 11. Example 3

A. Find the measure of SR. A. 22 B. 5.5 C. 11 D. 2.25 Example 3

B. Find the measure of HFI. C. 15 D. 30 Example 3

C. Find the measure of UV. A. 7 B. 14 C. 19 D. 25 Example 3

Concept

A. Find ST if S is the incenter of ΔMNP. Use the Incenter Theorem A. Find ST if S is the incenter of ΔMNP. By the Incenter Theorem, since S is equidistant from the sides of ΔMNP, ST = SU. Find ST by using the Pythagorean Theorem. a2 + b2 = c2 Pythagorean Theorem 82 + SU2 = 102 Substitution 64 + SU2 = 100 82 = 64, 102 = 100 Example 4

SU2 = 36 Subtract 64 from each side. Use the Incenter Theorem SU2 = 36 Subtract 64 from each side. SU = ±6 Take the square root of each side. Since length cannot be negative, use only the positive square root, 6. Since ST = SU, ST = 6. Answer: ST = 6 Example 4

B. Find mSPU if S is the incenter of ΔMNP. Use the Incenter Theorem B. Find mSPU if S is the incenter of ΔMNP. Since MS bisects RMT, mRMT = 2mRMS. So mRMT = 2(31) or 62. Likewise, mTNU = 2mSNU, so mTNU = 2(28) or 56. Example 4

mUPR + mRMT + mTNU = 180 Triangle Angle Sum Theorem Use the Incenter Theorem mUPR + mRMT + mTNU = 180 Triangle Angle Sum Theorem mUPR + 62 + 56 = 180 Substitution mUPR + 118 = 180 Simplify. mUPR = 62 Subtract 118 from each side. Since PS bisects UPR, 2mSPU = mUPR. This means that mSPU = mUPR. __ 1 2 Answer: mSPU = (62) or 31 __ 1 2 Example 4

A. Find the measure of GF if D is the incenter of ΔACF. B. 144 C. 8 D. 65 Example 4

B. Find the measure of BCD if D is the incenter of ΔACF. Example 4

End of the Lesson