derivative: can't get right ans. for Y(s) = (1/7s^2) - (7/s)

[mundah]

If Y(s) = (1/7s^2) - (7/s) what is Y'(s)?

I keep getting Y'(s) = (-14/s^3) + (7/s^2), but the website (this is online homework) keeps telling me its wrong. Am I missing something?

(p.s. for the way the problem is written, the library computer won't let me install any fonts or scripts!)

 

[mathstresser]

The way it looks to me you have 1/(7s^2)-7/s

so the derivative goes like this

for the first term you use the quotient rule:

(LDH-HDL)/L^2


((7s^2)(0)-(1)(14s))/((7s^2)^2)

the second term is just 7/s^2

that equals

-(14s)/(49/s^4) +7/s^2 which equals -(2)/(7s^3)+7/s^2

 

[mundah]

wow, i guess the negative was throwing me off. thank you so much!