If a curve is given by `x= a cos t + b/2 cos2t` and `y= asint + b/2 sin 2t`, then the points for which `(d^2 y)/dx^2 = 0`, are given by
A. `sintheta=(2a^(2)+b^(2))/(5ab)`
B. `tan theta=(3a^(2)+2b^(2))/(4ab)`
C. `costheta=-(a^(2)+2b^(2))/(3ab)`
D. none of these
