Question #27740

1 Answer
Gió
Jan 1, 2015

#(4,0)#

The function #f(x)=-2x^2+8x# represents a parabola and if you derive
it you get the slope of the tangent in every point #x#, so:
Derivative: #f'(x)=-4x+8#
If you want a slope of #-8# you need that:
#f'(x)=-4x+8=-8#
and solving for #x#:
#-4x=-16#
#x=4#
Substituting in #f(x)# you'll get the other coordinate #y#:
#y=f(4)=-2*16+32=0#

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