Question

Difference between squares of two numbers is 8. Twice the square of first number by square of second number is 19. What are the numbers?

Answer 1

3 & 1

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x^2-y^2=8 ------> (1)
2*x^2+y^2=19 ------> (2)

(1)+(2) => 3*x^2=27 => x^2=9 => x=3, y=1

Comments

what is wrong with this answer?

Answer 2

As soon as you see the phrase "difference between the squares" you should know exactly what to do. Use the difference of two squares formula:

a²-b²=(a-b)(a+b)

So we know (a+b)(a-b)=8. The only ways to factorise 8 are 1*8 and 2*4. You can't have a+b=8 and a-b=1 (since that would give 2b=9 and it's clear from context that were looking for whole numbers) so it must be a+b=4 and a-b=2. Therefore a=3 and b=1.