Now
contrapositive of this statement is ~ q ⇒ ~ p, i e , contrapositive of “ if f (x1) = f (x2),
then x1 = x2” is “if x1 ≠x2, then  f (x1) ≠ f (x2)” Now
x1 ≠ x2
⇒
2x1 ≠ 2x2
⇒
2x1+ 5 ≠ 2x2 + 5
⇒
f (x1) ≠ f (x2)