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Question

If a polynomial p(x)=x2ax+b has two zeroes 1 and 7, what is the value of ab?

A
8
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B
56
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C
42
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D
7
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Solution

The correct option is B 56
1 is a zero,
p(1)=0
12a+b=0
ab=1......eq (i)

Also,
7 is also a zero,
p(7)=0
72(7)a+b=0
7ab=49......eq (ii)

Subtracting (i) from (ii), we have
7aba+b=48
6a=48
a=8

Substituting a=8 in eq (i), we have
8b=1
b=7

ab=(8)(7)=56

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