How to find the angle of two lines - PSAT Math

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Question

Pythagoras

Refer to the above figure. You are given that and . Which of the following statements would be sufficient to prove that is a right angle, given what is already known?

I)

II) and are both acute

III) is a right angle

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Answer

If , then has short sides and long side . Since

,

then, by the converse of the Pythagorean Theorem, is a right triangle with right angle . Statement I is sufficient.

If and are both acute,we know nothing about ; every triangle has at least two acute angles regardless of type. Statement II tells us nothing.

and form a linear pair and are therefore supplementary. If one is a right angle, so is the other. Therefore, if is a right angle, so is . Statement III is sufficient.

The correct response is Statement I and III only.

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