Topic Details (Notes format)

How to Calculate Modular Inverses

Subject: Mathematics

Book: Maths Mastery

A modular inverse of a number a (mod m) is x such that ax ≡ 1 (mod m). It exists only if gcd(a,m)=1. The Extended Euclidean Algorithm finds x for which ax + my=1, implying ax≡1 (mod m). For instance, to find the inverse of 3 modulo 7, we solve 3x + 7y=1, yielding x=5 because 3×5=15≡1 (mod 7). Modular inverses power encryption algorithms (RSA), solve congruences, and handle advanced computations in computer science. Mastery ensures you can manipulate modular arithmetic quickly for a wide range of cryptographic and number-theoretic tasks.

Practice Questions

The LCM of two numbers is 60, and their HCF is 5. If one of the numbers is 20, what is the other number?

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If the product of two numbers is 120 and their sum is 26, what are the numbers?

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If 8x = 512, what is the value of x?

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What is the sum of all odd numbers from 1 to 99?

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If 5x - 2 = 13, what is the value of x?

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If the sum of the angles of a polygon is 1080°, how many sides does the polygon have?

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A rectangle has an area of 48 cm² and a length of 8 cm. What is its width?

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If x:y = 4:5 and y:z = 2:3, what is x:z?

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If a+b = 10 and ab = 21, what is the value of a^3 + b^3?

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If the sum of three consecutive integers is 96, what are the integers?

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