section_path: History/Medieval/India
section_name: India
paragraph_text: India
  
  Bhāskara II (c.1114–1185) was acquainted with some ideas of differential calculus and suggested that the "differential coefficient" vanishes at an extremum value of the function. In his astronomical work, he gave a procedure that looked like a precursor to infinitesimal methods. Namely, if x ≈ y {\displaystyle x\approx y} then sin (y) − sin (x) ≈ (y − x) cos (y). {\displaystyle \sin(y)-\sin(x)\approx (y-x)\cos(y).} This can be interpreted as the discovery that cosine is the derivative of sine. In the 14th century, Indian mathematicians gave a non-rigorous method, resembling differentiation, applicable to some trigonometric functions. Madhava of Sangamagrama and the Kerala School of Astronomy and Mathematics stated components of calculus, but according to Victor J. Katz they were not able to "combine many differing ideas under the two unifying themes of the derivative and the integral, show the connection between the two, and turn calculus into the great problem-solving tool we have today".