SOLUTION: For this problem you may want to recall that if y=sinh(x), then dy/dx=cosh(x), and d^(2)y/dx^(2)=sinh(x). It can be shown that y1=sinh(3x), y2=cosh(3x) and y3=e^(3x) are solutio

Algebra ->  Equations -> SOLUTION: For this problem you may want to recall that if y=sinh(x), then dy/dx=cosh(x), and d^(2)y/dx^(2)=sinh(x). It can be shown that y1=sinh(3x), y2=cosh(3x) and y3=e^(3x) are solutio      Log On


   



Question 1184638: For this problem you may want to recall that if y=sinh(x), then dy/dx=cosh(x), and d^(2)y/dx^(2)=sinh(x).
It can be shown that y1=sinh(3x), y2=cosh(3x) and y3=e^(3x) are solutions to the differential equation xD^(3)y−8D^(2)y−9xDy+72y=0 on (0,∞).
a)
What does the Wronskian of y1,y2,y3 equal on (0,∞)?
W(y1,y2,y3)=______________________ on (0,∞).
b)
Is {y1,y2,y3} a fundamental set for xD^(3)y−8D^(2)y−9xDy+72y=0 on (0,∞)?
Yes or No

Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!

a) .
***This is expected since the set { y%5B1%5D, y%5B2%5D, +y%5B3%5D} is linearly dependent, because y%5B1%5D+%2B+y%5B2%5D+=+sinh%283x%29+%2B+cosh%283x%29+=+e%5E%283x%29=y%5B3%5D.

b) No, { y%5B1%5D, y%5B2%5D, +y%5B3%5D} is not a fundamental set for the D.E. (i.e., it cannot be a basis for the solutions of the D.E.).