  This paper introduces DD calculus and describes the basic calculus concepts
of derivative and integral in a direct and non-traditional way, without limit
definition: Derivative is computed from the point-slope equation of a tangent
line and integral is defined as the height increment of a curve. This direct
approach to calculus has three distinct features: (i) it defines derivative and
(definite) integral without using limits, (ii) it defines derivative and
antiderivative simultaneously via a derivative-antiderivative (DA) pair, and
(iii) it posits the fundamental theorem of calculus as a natural corollary of
the definitions of derivative and integral. The first D in DD calculus
attributes to Descartes for his method of tangents and the second D to DA-pair.
The DD calculus, or simply direct calculus, makes many traditional notations
and procedures unnecessary, a plus when introducing calculus to the
non-mathematics majors. It has few intermediate procedures, which can help
dispel the mystery of calculus as perceived by the general public. The
materials in this paper are intended for use in a two-hour introductory lecture
on calculus.
