Answer
$3.85 \ cm$
Work Step by Step
Since we have a right triangle with legs a, b and the hypotenuse c, then by the Pythagorean theorem, we have $$c^2=a^2+b^2.$$
Then the hypotenuse is given by
$$
c=\sqrt{a^2+b^2}=\sqrt{1.72^2+3.44^2}=3.85 \ cm
.$$
