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secondary 4 | A Maths
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someone pls help me with b
if a cubic graph have 2 x-intercepts, it means that ...
1 intercept is a "single root" and
the other intercept is a "repeated root".
assuming that x=1 is the "single root", then following the method provided by sstrike below, k=16 and the "repeated root" is at x=-4.
if x=1 is the "repeated root", then the quadratic factor can be factorised to ...
(x-1)(x-p) where p is the "single root".
by expanding (x-1)(x-p) and comparing terms, gives p=-9 and k=-9.
therefore, 2 possible answers ...
k=16 (gives x-intercepts at x=1 & x=-4 (repeated)
or
k=-9 (gives x-intercepts at x=-9 & x=1 (repeated).
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this is the correct one. thx Chau again.