Direct Proof Basics: From Hypothesis to Conclusion

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Alva Benedict B., PhD
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Alva Benedict B. is an experienced mathematician and math content developer with over 15 years of teaching and tutoring experience across high school, undergraduate, and test prep levels. He specializes in Algebra, Calculus, and Statistics, and holds advanced academic training in Mathematics with extensive expertise in LaTeX-based math content development.
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1) What is the first step in a direct proof of "If P, then Q"?

Explanation

In a direct proof of a conditional statement "If P, then Q", the goal is to show that P implies Q. The first step is to assume that P is true. Then, using logical deductions, definitions, and known facts, we derive that Q must be true. This approach directly establishes the implication.

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About This Quiz
Direct Proof Basics: From Hypothesis To Conclusion - Quiz

Are you ready to see how formal proofs actually work step by step? In this quiz, you’ll practice the core idea of a direct proof: start by assuming the hypothesis is true and then use logic, definitions, and simple algebra to reach the conclusion. You’ll work with even and odd... see morenumbers, divisibility, and basic inequalities to see how each statement flows into the next. By the end, you’ll feel more confident reading and writing direct proofs without feeling lost in symbols!
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2) In a direct proof of "If n is even, then n² is even," what do we assume first?

Explanation

For a direct proof, we start by assuming the hypothesis. Here, the hypothesis is that n is even. So, we assume n is even, meaning n = 2k for some integer k. Then, we compute n² = (2k)² = 4k² = 2(2k²), which is even, thus deriving the conclusion.

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3) Which statement best describes a direct proof?

Explanation

A direct proof involves starting with the given hypotheses or premises and then using logical steps, definitions, and theorems to directly arrive at the conclusion. This method does not involve assuming the negation or using contrapositive, but rather builds a chain of reasoning from the assumptions to the conclusion.

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4) In a direct proof of "If x > 0, then x² > 0," we start by assuming:

Explanation

In a direct proof, we assume the hypothesis. Here, the hypothesis is x > 0. Since x is positive, multiplying both sides by x (which is positive) gives x² > 0, thus directly proving the statement.

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5) Which of these is NOT a characteristic of a direct proof?

Explanation

A direct proof relies on logical implications from the hypothesis to the conclusion and does not use contradiction. Using contradiction is a feature of proof by contradiction, where we assume the negation of the conclusion and derive a false statement.

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6) To prove "If a number is divisible by 4, then it is even" directly, we start by:

Explanation

In a direct proof, we assume the hypothesis. Here, the hypothesis is that the number is divisible by 4. From this, we can show that since 4 is a multiple of 2, the number is also divisible by 2, meaning it is even.

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7) In a direct proof of "If n is odd, then n+1 is even," the first line should be:

Explanation

The first step in a direct proof is to assume the hypothesis. Here, the hypothesis is that n is odd. Therefore, we begin with "Assume n is odd." Then, since n is odd, n+1 is even, which can be shown directly.

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8) Which proof technique directly shows P → Q by assuming P and deriving Q?

Explanation

Direct proof is the technique where we assume P is true and then through logical steps derive that Q is true. This directly establishes the implication P → Q. Other techniques like contradiction or contrapositive do not involve assuming P and deriving Q directly.

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9) To directly prove "If x and y are even, then x+y is even," we begin by:

Explanation

In a direct proof, we start with the hypothesis that x and y are even. This means x = 2a and y = 2b for some integers a and b. Then, x+y = 2a + 2b = 2(a+b), which is even, thus proving the statement.

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10) What is the correct format for the first line of a direct proof of "If A, then B"?

Explanation

The standard first line in a direct proof of "If A, then B" is to assume that A is true. This sets up the hypothesis, and then we proceed to show that B must be true under this assumption.

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11) In a direct proof that "If n is divisible by 6, then n is divisible by 3," what do we assume first?

Explanation

For a direct proof, we assume the hypothesis, which is that n is divisible by 6. Since 6 is divisible by 3, it follows that n is also divisible by 3, thus proving the conclusion.

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12) In a direct proof of "If a = b and b = c, then a = c," we start by:

Explanation

This is a direct proof of the transitive property of equality. We start by assuming the hypothesis, which is that a = b and b = c. Then, by substitution, we can conclude that a = c.

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13) Which of these statements is best suited for a direct proof?

Explanation

Direct proofs are well-suited for conditional statements of the form "If P, then Q" where we can assume P and derive Q through logical steps. The statement "If n is even, then n² is even" is such a conditional statement and can be proven directly by assuming n is even and showing n² is even.

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14) To directly prove "If x is rational and y is rational, then x+y is rational," we begin by:

Explanation

In a direct proof, we assume the hypothesis that x and y are rational. We use the definition of rational numbers, this means x = a/b and y = c/d for some integers a,b,c,d with b,d ≠ 0. Then, x+y = (ad + bc)/(bd), which is rational, thus proving the statement.

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15) In the direct proof that "If n is a multiple of 4, then n² is a multiple of 16," what is the first assumption?

Explanation

We start by assuming the hypothesis that n is a multiple of 4, which means n = 4k for some integer k. Then, n² = (4k)² = 16k², which is a multiple of 16, thus proving the conclusion.

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Alva Benedict B. |PhD
College Expert
Alva Benedict B. is an experienced mathematician and math content developer with over 15 years of teaching and tutoring experience across high school, undergraduate, and test prep levels. He specializes in Algebra, Calculus, and Statistics, and holds advanced academic training in Mathematics with extensive expertise in LaTeX-based math content development.
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What is the first step in a direct proof of "If P, then Q"?
In a direct proof of "If n is even, then n² is even," what do we...
Which statement best describes a direct proof?
In a direct proof of "If x > 0, then x² > 0," we start by...
Which of these is NOT a characteristic of a direct proof?
To prove "If a number is divisible by 4, then it is even" directly, we...
In a direct proof of "If n is odd, then n+1 is even," the first line...
Which proof technique directly shows P → Q by assuming P and...
To directly prove "If x and y are even, then x+y is even," we begin...
What is the correct format for the first line of a direct proof of "If...
In a direct proof that "If n is divisible by 6, then n is divisible by...
In a direct proof of "If a = b and b = c, then a = c," we start by:
Which of these statements is best suited for a direct proof?
To directly prove "If x is rational and y is rational, then x+y is...
In the direct proof that "If n is a multiple of 4, then n² is a...
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