Question 1192924
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Replace every x with x+h
{{{f(x)=-3x+7}}}


{{{f(x+h)=-3(x+h)+7}}}


{{{f(x+h)=-3x-3h+7}}}


Then compute the difference quotient.
{{{(f(x+h)-f(x))/h = ((-3x-3h+7)-(-3x+7))/h}}}


{{{(f(x+h)-f(x))/h = (-3x-3h+7+3x-7)/h}}}


{{{(f(x+h)-f(x))/h = (-3h)/h}}}


{{{(f(x+h)-f(x))/h = -3}}}
The idea is that h does not equal zero, but it gets closer and closer to it. 
This is where the concept of limits come in.
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