Page 90 - Math Course 1 (Book 2)

Geometry: Angles

Key Concept Congruent Angles

Name right angle acute angle obtuse angle

Measure m ∠A = 90 m ∠B < 90 180 > m ∠C > 90

This symbol
means a 90 o
Model angle

A B C

∠GBH ≌ ∠HCI Given
Let’s Begin
m∠GBH ≌ m∠HCI Def nition of congruent angles.

2x + 5 = 3x – 10 Substitution
Use Algebra to Find Angle Measures 2x + 15 = 3x Add 10 to each side.

Examples 15 = x Subtract 2x from each side.

INTERIOR DESIGN Use the value of x to f nd the measure of one angle.
Wall stickers of standard shapes are often used
to provide a stimulating environment for a young m∠GBH = 2x + 5 Given
child’s room. A f ve-pointed star sticker is shown
with vertices labeled. = 2(15) + 5 x = 15

= 30 + 5 or 35 Simplify.

Simplify m∠GBH = m∠HCI, m∠HCI = 35.

Both ∠GBH and ∠HCI
Answer
measure 35.

Find m∠GBH and m∠HCI if ∠GBH ≌ ∠HCI,
m∠GBH = 2x + 5, and m∠HCI = 3x – 10.

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