The equation has a unique solution, if x, y are :
(A) Natural numbers
(B) Positive real numbers
(C) Real numbers
(D) Rational numbers
Answer:
(A) Natural numbers
Solution:
Unique solution: for Unique solution, there should exist only one pair of x and y.
In natural numbers, there exists only one pair which is (1, 1)
2x + 5y = 7
(2) + (5) = 7
7 = 7
In positive real numbers there exists more than one pair.
For example: (0.5, 1.2), (1.5, 0.8)…
In real numbers there exists more than one pair.
For example: (–0.5, 1.6), (–1.5, 2)…
Also in rational numbers, there exists more than one pair.
For example:
…
Hence in natural numbers there exists only one pair therefore the solution is natural numbers.