The correct answer is: [D]: "supplementary angles, 180° " .
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Note:
Choices:
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[B]: "complementary angles, 180° " ; and:
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[C]: "supplementary angles, 90° " ;
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can automatically be ruled out ; since by definition:
→ Complementary angles always add up to 90° — NOT 180° ;
and: supplementary angles always add up to 180° — NOT 90° .
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Note: "Adjacent angles" refer to "supplementary angles" ; which, by definition add up to 180° . Futhermore, looking at the image provided,
we see that ∠1 and ∠2 are, in fact "adjacent" and that ∠1 and ∠2 comprise the entire portion of a "straight line" (being intersected by a transversal)" ;
and as such; ∠1 and ∠2 are supplementary angles—
and as such—add up to 180° .
(which rules out: Choice [A]: "complementary angles, 90°) ;
→ and demonstrates the correct answer:
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Answer choice: [D]: "supplementary angles, 180° " .
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