I don't have a cool name for this

Algebra Level 3

If x 2 + p x 444 p = 0 x^2 + px - 444p = 0 has integral roots where p is a prime number , then find the value of p


The answer is 37.

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4 solutions

Adrian Neacșu
Apr 9, 2014

I have a proper solution. The roots are integers. We know that x+y=-p and xy=444p. So xy is a multiple of p. But p divides xy if p divides either x or y. Let's say that p divides x. Which means that x=np, but we know that x+y=-p which gives that y=-p-np=-(n+1)p. Now we'll use the product: xy=444p. Which means that -n(n+1)p^2=444p. Which means that p^2 divides 444p, which gives p divides 444. Since p is prime and a divisor of 444 then p can only be 2, 3 or 37. Then plug those values of p in the equation and check if the roots are integers. The discriminant is a square number only when p=37. The other solutions are incomplete or simple guesses.

Mas Mus
May 20, 2014

We can rewrite the equation in two other forms, as : x 2 + p x + ( 148 ) × 3 p = 0 x^{2}+px+(-148) \times3p=0 or x 2 + p x + 148 × ( 3 p ) = 0 x^{2}+px+148 \times(-3p)=0 . It is clear that 148 + 3 p = p -148+3p=p and 148 + ( 3 p ) = p 148+(-3p)=p , then we get p = 74 p=-74 and p = 37 p=37 respectively. Since p p is prime, hence p = 37 \boxed{p=37} .

Divyam Bapna
Mar 2, 2014

Simple middle term splitting method can help to solve it x^2 +px-444p=0 444=37×4×3×p 37×4-3p=p p=37

Tanya Gupta
Mar 2, 2014

I have no proper solution...Discriminant id p^2+1776p...Use a calculator and keep substituting primes to make it a perfect square....personally...i dont think the question to be "cool"...is there a better way??

I did the same thing.

Danyal Ahmad - 7 years, 3 months ago

i also did the same thing there was nothing cool in this problem

Rohan Kumar - 7 years, 3 months ago

even 222 can be the answer

Chirag Jalan - 7 years, 2 months ago

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Its mentioned that p is a prime number...222 is not...

Tanya Gupta - 7 years, 2 months ago

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