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If two angles are supplementary, then their angle measures add up to 180^(∘).
180^(∘), substitution, 90^(∘), 90 ^(∘)
In the exercise we are given the following figure, including angles 1 and 2.
We are asked to complete the following paragraph proof.
| Given | m ∠ 1 = m ∠ 2, ∠ 1 and ∠ 2 are supplementary. |
|---|---|
| Prove | ∠ 1 and ∠ 2 are right angles. |
| Proof | m ∠ 1 + m ∠ 2= since they are supplementary angles. Since m ∠ 1 = m ∠ 2, then m ∠ 1 + m ∠ 1=180^(∘) by . Solving the equation gives m ∠ 1 = . Since m ∠ 1 = m ∠ 2, then m∠ 2 is also . Therefore, ∠ 1 and ∠ 2 are right angles. |
Let's do it! First, if two angles are supplementary, then by definition their angle measures add up to 180^(∘). We can fill in the first gap.
| Given | m ∠ 1 = m ∠ 2, ∠ 1 and ∠ 2 are supplementary. |
|---|---|
| Prove | ∠ 1 and ∠ 2 are right angles. |
| Proof | m ∠ 1 + m ∠ 2= 180^(∘) since they are supplementary angles. Since m ∠ 1 = m ∠ 2, then m ∠ 1 + m ∠ 1=180^(∘) by . Solving the equation gives m ∠ 1 = . Since m ∠ 1 = m ∠ 2, then m∠ 2 is also . Therefore, ∠ 1 and ∠ 2 are right angles. |
Now, we can rewrite the second sentence of the proof using mathematical symbols. m ∠ 1 = m ∠ 2 ⇒ m ∠ 1 + m ∠ 1=180^(∘) We see that m ∠ 1 was substituted for m ∠ 2 in the expression. The resulting statement is still true because the angle measures are equal.
| Given | m ∠ 1 = m ∠ 2, ∠ 1 and ∠ 2 are supplementary. |
|---|---|
| Prove | ∠ 1 and ∠ 2 are right angles. |
| Proof | m ∠ 1 + m ∠ 2= 180^(∘) since they are supplementary angles. Since m ∠ 1 = m ∠ 2, then m ∠ 1 + m ∠ 1=180^(∘) by substitution. Solving the equation gives m ∠ 1 = . Since m ∠ 1 = m ∠ 2, then m∠ 2 is also . Therefore, ∠ 1 and ∠ 2 are right angles. |
| Given | m ∠ 1 = m ∠ 2, ∠ 1 and ∠ 2 are supplementary. |
|---|---|
| Prove | ∠ 1 and ∠ 2 are right angles. |
| Proof | m ∠ 1 + m ∠ 2= 180^(∘) since they are supplementary angles. Since m ∠ 1 = m ∠ 2, then m ∠ 1 + m ∠ 1=180^(∘) by substitution. Solving the equation gives m ∠ 1 = 90^(∘). Since m ∠ 1 = m ∠ 2, then m∠ 2 is also . Therefore, ∠ 1 and ∠ 2 are right angles. |
Because angles 1 and 2 have the same measure, we know that m∠ 2 is also 90^(∘).
| Given | m ∠ 1 = m ∠ 2, ∠ 1 and ∠ 2 are supplementary. |
|---|---|
| Prove | ∠ 1 and ∠ 2 are right angles. |
| Proof | m ∠ 1 + m ∠ 2= 180^(∘) since they are supplementary angles. Since m ∠ 1 = m ∠ 2, then m ∠ 1 + m ∠ 1=180^(∘) by substitution. Solving the equation gives m ∠ 1 = 90^(∘). Since m ∠ 1 = m ∠ 2, then m∠ 2 is also 90^(∘). Therefore, ∠ 1 and ∠ 2 are right angles. |
Our paragraph proof is now complete.