Starting with p, we deduce p ⇒ r ⇒ s ⇒ … ⇒ q This implies that “p ⇒ q” is true Example 2 Prove that the function f : R →
→
→
→
→ R
defined by f (x) = 2x + 5 is one-one Solution Note that a function f is one-one if
f (x1) = f (x2) ⇒ x1 = x2  (definition of one-one function)
Now,  given that
f (x1) = f (x2), i