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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. |
| 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. |
To solve the resulting equation, we should isolate m ∠1 on one side of the equation. Let's do it!
We found that m ∠1=90^(∘). Let's write that down.
| 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.