x 2 − p x + q = 0
Consider the quadratic equation above where p and q are prime numbers.
Given that this equation has all positive integral roots, find the value of ( p 3 + q 3 ) ( p − q + 1 ) .
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Nice solution
Good logical solution.Hope we will get such tricky problems in future!
Nice solution
Same here!
It is given that the roots are positive and integral.
(x^{2} + q = px
Here, x has to be positive and integral. We observe that the square of x + (a prime number) is divisible by x to satisfy the equation.
That is only possible when x is 1 or equal to q for positive integral value.
This gives us that q+1=p or q^2 + q=p
When x=1, p=3 and q=2.
So answer for this question is 70.
hi panda!!!!! @RWIT PANDA
Log in to reply
Sorry I can't recognize u
Log in to reply
actually in school you studied previously i was also there but in different section..i know u
Log in to reply
@Sakshi Rathore – R u talking of RIS navi mumbai?
Log in to reply
@Rwit Panda – yes.....I'm right is it you???
Problem Loading...
Note Loading...
Set Loading...
Let a and b be the roots of the equation.
⇒ a + b = p and a b = q
Since q is prime, either of a and b must be 1 and the other equal to q
Assume that a = 1 and b = q
⇒ q + 1 = p
From this equation its clear that either of p or q must be even and the other odd , but p and q are primes , so
⇒ p = 3 and q = 2
⇒ ( p 3 + q 3 ) ( p − q + 1 ) = 7 0