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Homework Statement
Find the derivative from first principles, i.e, from the definition of f ' as a limit, for f(x)= [tex]\sqrt{}a-bx, where a and b are positive constants. What are the domains of f and f ' ?
The Attempt at a Solution
I solved:
f(x) = \sqrt{a-bx} ---> f(x+h) = \sqrt{a-b(x+h)}
lim h-->0 = \sqrt{a-b(x+h)} - \sqrt{a-bx} / h
lim h-->0 = \sqrt{a-bx+bh-a+bx} / h
lim h-->0 = \sqrt{bh} / h
lim h-->0 = \sqrt{bh}* \sqrt{bh} / h\sqrt{bh}
lim h-->0 = b/ \sqrt{bh}
What did I do wrong here?
Please help and thanks
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