Difference between Perfect Squares

Algebra Level 2

Given that a 2 b 2 = 501 { a }^{ 2 }-{ b }^{ 2 }=501 and a a and b b are consecutive positive integers where a > b a>b , what is the value of b b ?


The answer is 250.

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3 solutions

since a > b a>b , a = b + 1 a=b+1

a 2 b 2 = 501 a^2-b^2=501

substitute:

( b + 1 ) 2 b 2 = 501 (b+1)^2-b^2=501

b 2 + 2 b + 1 b 2 = 501 b^2+2b+1-b^2=501

2 b = 500 2b=500

b = 250 b=250

Why a= b + 1??

Julia Christine - 4 years, 5 months ago

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According to the question, a>b that means a is greater than b and a, b are consecutive positive integers.. Like 5 , 6 ; 30 , 31 ; 58 , 59 5,6 ; 30,31; 58,59 etc..

Prokash Shakkhar - 4 years, 5 months ago

because a is greater than b, and a and b are consecutive positive integers. that means that their difference is 1.

A Former Brilliant Member - 4 years, 5 months ago

Why can't the division be in form of 167 & 3, where a=85 & b= 82 ?

A Former Brilliant Member - 4 years, 1 month ago
Sharky Kesa
Dec 27, 2016

a a and b b are consecutive positive integers, with a > b a>b , so a b = 1 a-b=1 . Thus

a 2 b 2 = 501 ( a + b ) ( a b ) = 501 a + b = 501 a b = 1 2 b = 500 b = 250 \begin{aligned} a^2 - b^2 &= 501\\ (a+b)(a-b) &= 501\\ \implies a+b &= 501\\ a-b &= 1\\ \implies 2b &= 500\\ b&= 250\\ \end{aligned}

Aaryan Vaishya
Dec 5, 2018

a^2-B^2=501,so a+B=501(proof at the end),or B+(B+1)=501(The problem mentioned the numbers were consecutive,so a=B+1).Solving,we get B=250(B=B+1=501,B+B=500,2B=500,B=250).PROOF(involves good understanding of multiplication):Let's say a=B+1.So,to get from B^2 to a^2,we add B(there are now B+1(or a)groups of B).Then we switch the terms and add a(there are now B+1 B+1s or a sets of a or a^2).As you see,we added an a and a B to go from b^2 to a^2.Therefore a^2-b^2=a+b.You can actually generalize my proof to any number of consecutive numbers.For that the formula is a^2-b^2(where a=b+n)=b+2(b+1+b+2+b+3....b+(n-1))+a.Try proving it yourself!

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