The transverse axis of a hyperbola is of length 2a and a vertex divides the segment of the axis between the centre and the corresponding focus in the ratio 2 : 1, then the equation of the hyperbola is
a. 4x2−5y2=4a2
b. 4x2−5y2=5a2
c. 5x2−4y2=4a2
d. 5x2−4y2=5a2