EXAMPLE 4Find the derivative of the function

f(x) =x²8x+7

at the numbera. SOLUTIONFromthe definitionwe have

f'(a)	=	limh0 f(a+h)f(a) h
	=	limh0 8(a+h) +7 [a28a+7] h
	=	limh0 a2+ 8a8h+7a2+8a7 h
	=	limh0 h
	=	limh0
	=	.