d) (a, b) = 21⇒ a = 21x, b= 21y, (x, y) = 1
a + b = 231 ⇒ 21x + 21y = 231 |:21 ⇒ x + y = 11
I) x = 1, y = 10 ⇒ a = 21, b = 210
II) x = 2, y = 9⇒ a = 42, b = 189
III) x = 3, y = 8 ⇒ a = 63, b = 168
IV) x = 4, y = 7⇒
V) x = 5, y = 6⇒
VI) x = 6, y = 5⇒
VII) x = 7, y = 4⇒
VIII) x = 8, y = 3⇒
IX) x = 9, y = 2⇒
X) x = 10, y = 1 ⇒ x = 210, y = 21