Envelope of a family of curves can be defined as __________
(a) A curve which touches 50% of the family of curves
(b) A curve which is a straight line
(c) A curve which touches each member of the family of curves
(d) A curve which surrounds the family of curves
I have been asked this question by my college professor while I was bunking the class.
This question is from Envelopes topic in portion Differential Calculus of Engineering Mathematics