Question 1118669
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It's quite clear what your question is.  Unfortunately, there are a few "tutors" here who like to increase the number of questions they have "answered" by being nitpickers about how you present the problem.<br>
f(x) = x^2-7x; f(a) = f(-8) = 64+56 = 120<br>
f'(x) = 2x-7; f'(a) = f'(-8) = -16-7 = -23<br>
The point of tangency is (-8,120); the slope at that point is -23.  The equation is<br>
{{{y-120 = -23(x-(-8))}}}
{{{y-120 = -23(x+8)}}}
{{{y = -23(x+8)+120}}}<br>
There are of course many different forms in which this equation can be shown.