GMAT Math : DSQ: Calculating whether right triangles are congruent

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Example Question #11 :Right Triangles

Given:and, with right angles

True or false:.

Statement 1:

Statement 2:

Possible Answers:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

两个表述一起不足以方法r the question

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question..

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

Assume Statement 1 only. By the Pythagorean Theorem,, so; subsequently,, and one side congruence is proved. However, this, along with one angle congruence - the congruence of right anglesand- is not enough to prove or disprove triangle congruence.

Assume Statement 2 only. By the Pythagorean Theorem,. Since, it follows that, and, subsequently,. Since, if,, it follows by contradiction thatis a false statement.

Example Question #12 :Right Triangles

Given:and, with right angles

True or false:.

声明1:一种罪恶gle circle can be constructed that passes throughand.

Statement 2:

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

两个表述一起不足以方法r the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone is true. Since each right triangle is inscribed inside a circle, each of the right angles is inscribed in that circle, and each intercepts a semicircle. That makes the two hypotenuses of the triangles,and, diameters; since they are on thesamecircle, their lengths are the same. However, no information is given about any of the other sides or angles, so no congruence can be proved or disproved.

Statement 2 alone gives us only congruence between one set of corresponding legs, which, along with one angle congruence, is insufficient to prove or to disprove triangler congruence.

Now assume both statements are true. From Statement 1, it follows that congruence of hypotenuses, and Statement 2 gives us congruence of corresponding legs; this sets up the conditions of the Hypotenuse-Leg Theorem, so it follows that.

Example Question #13 :Right Triangles

Given:and, with right angles

True or false:.

Statement 1:andhave the same area.

Statement 2:

Possible Answers:

两个表述一起不足以方法r the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

两个表述一起不足以方法r the question.

Explanation:

Assume both statements are true. We show that both statements are insufficient to answer the question.

Supposeand.

and, satisfying the conditions of Statement 2.

The area of a right triangle is half the product of the lengths of its legs. Each triangle therefore has as its area, making the areas the same; Statement 1 is satisfied.

Since corresponding legs of the triangles are congruent,by the Side-Angle-Side Postulate.

Now, supposeand.

and, satisfying the conditions of Statement 2.

The area of a right triangle is half the product of the lengths of its legs. Each triangle therefore has as its area, making the areas the same; Statement 1 is satisfied.

However,and, so it is not true that.

Example Question #14 :Right Triangles

Given:and, with right angles

True or false:.

Statement 1:

Statement 2:

Possible Answers:

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

两个表述一起不足以方法r the question.

Correct answer:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

Assume Statement 1 alone. The statement gives that all four legs of both triangles are congruent - specifically,and. Since the right angles are also congruent, then, by the Side-Angle-Side Postulate,.

Assume Statement 2 alone. The statement gives that all four acute angles are congruent - specifically, thatand. However, since we do not have any congruence or noncongruence between corresponding sides, congruence of the triangles cannot be proved or disproved.

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