Big Ideas Math: Modeling Real Life, Grade 7
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5. Finding Unknown Angle Measures
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Exercise 32 Page 395

If three adjacent angles in the diagram form a straight angle, we know that that the sum of their measures equals 180^(∘).

∠ FGL=10^(∘), ∠ KGJ=80 ^(∘)

Practice makes perfect

Let's consider the given diagram.

We see that we have three adjacent angles that sum to the straight angle ∠ JGF. Therefore, the sum of their measures equals the measure of ∠ JGF — 180^(∘). Let's write this fact as an equation for x. Also, note that the measure of ∠ KGL is 90^(∘). x^(∘)+ 90^(∘) + 8x^(∘) = 180^(∘) Let's solve the above equation!
x^(∘)+90^(∘) + 8x^(∘) = 180^(∘)
9x^(∘) + 90^(∘) = 180^(∘)
9x^(∘) = 90^(∘)
x^(∘) = 10^(∘)
We found that x^(∘) = 10^(∘). Now, we will substitute x^(∘)=10^(∘) into the angle 8x^(∘) to find its exact value.
8x^(∘)
8( 10)^(∘)
80 ^(∘)
Finally, let's list the found angle measurements. ∠ FGL=10^(∘) and ∠ KGJ=80 ^(∘)