The equation is given as,
y= c 1 e x + c 2 e −x
Differentiate both sides of above equation with respect to x,
d dx ( y )= d dx ( c 1 e x + c 2 e −x ) y ′ = c 1 e x − c 2 e −x
Again differentiate above equation with respect to x,
d dx ( y ′ )= d dx ( c 1 e x − c 2 e −x ) y ″ = c 1 e x + c 2 e −x d 2 y d x 2 =y d 2 y d x 2 −y=0
Therefore, option B is correct.