The efficiency rating, E, of a particular spark plug when
the gap is set at x mm is said to be 400(x – x2).
a Sketch the graph of E against x for 0 < x < 1.
b What values of x give a zero efficiency rating?
C What value of x gives the maximum efficiency rating?
d Use the graph, or otherwise, to determine the values of
x between which the efficiency rating is 70 or more.

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mrbilldoesmath!

answer: a parabola

steps:

(x-1)(x+4)   = x(x+4) - 1(x+4) = (x^2 + 4x) - (x+4)

                = x^2 +4x -x -4   = x^2 +3x -4

which is a parabola

mrb

point m is on plane r