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Glencoe Math: Course 3, Volume 2

GM

Glencoe Math: Course 3, Volume 2 View details

3. Angles of Triangles

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Exercise 1 Page 392

The sum of the measures of the interior angles of a triangle is $18 0^{\circ} .$

$4 5^{\circ}$

Practice makes perfect

We want to find the measure of the angle in the given triangle.

A triangle with two known interior angles measuring 75 and 60 degrees, and the other interior angle measuring x degrees.

To find this angle measure, we will first recall a key piece of information!

Angle Sum of a Triangle
The sum of the measures of the interior angles of a triangle is $18 0^{\circ} .$

With this rule, we can write an equation connecting the measures of the angles of our triangle.

x^{\circ} + 7 5^{\circ} + 6 0^{\circ} = 18 0^{\circ}

Let's solve the equation and find the value of

x .

For simplicity, we will not write the degree symbol.

x + 75 + 60 = 180

▼

Solve for

x

Add terms

x + 135 = 180

$LHS - 135 = RHS - 135$

x = 45

The measure of the third angle is

4 5^{\circ} .

triangle

Subchapter links

Guided Practice p.392

Independent Practice p.393-394

H.O.T. Problems p.394

Standardized Test Practice p.394-396

Extra Practice p.395

Common Core Review p.396