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If f(7) = -5, g(7) = 2, f'(7) = 3, and g'(7) = -1, find (2f.3g)'(7). Show your calculation.
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The correct solution is THIS:
(2f.3g)'(7) = 2f'(7)*3g(7) + 2f(7)*3g'(7) = (2*3)*(3*2) + (2*(-5))*(3*(-1)) = 66.
It uses standard formula for derivative of a product
(u*v)' = u'*v + u*v'.
The tutor @greenestamps misread the problem and inadvertently gave incorrect solution.