For x , y , z to be prime numbers, what is the total number of ordered triplets ( x , y , z ) which satisfy equation x y + 1 = z ?
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.
@Sandeep Bhardwaj how about this?
Log in to reply
Its also cool. :)
The only ordered pair is ( 2 , 2 , 5 )
Hint :
x,y, and z are prime numbers and prime numbers can be odd numbers only (except 2)
( o d d ) o d d = o d d .
o d d + 1 = e v e n = z ( n o t p o s s i b l e ) except 2
!!!
Log in to reply
Because it is given that x,y,z are all prime numbers. You are taking x=1, but 1 is not a prime number. got it ?
x,y, and z are prime numbers and prime numbers can be odd numbers only (except 2) answer is (2,2,5)
Problem Loading...
Note Loading...
Set Loading...
We know that x y + 1 y = z = prime.Now,as long as y = o d d x y + 1 y which is a prime is divisible by x + 1 which is even (excluding 2 ).Thus, y = even.Now,the only possible case is when y = 2 . ⟹ x 2 + 1 = z . But as long as x = odd and z = odd,this can't happen.Thus,the only possible case is when x = 2 . Putting x = 2 in the first equation gives z = 5 . Thus,the only possible triplet x , y , z = 2 , 2 , 5 .