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Question

If(x3+ax2+bc+6) has (x-2) as a factor and leaves a remainder 3 when divided by (x-3), find the value of a and b.

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Solution

Dear student,

Let p(x) = x³ + ax²+ bx +6

(x-2) is a factor of the polynomial x³ + ax² + b x +6

p(2) = 0

p(2) = 2³+ a.2² + b.2 +6 =8+4a+2b+6 =14+ 4a+ 2b = 0

7 +2 a +b = 0


b =-7-2a→(i)

x³+ ax²+ bx +6 when divided by (x-3) leaves remainder 3.

p(3) = 3

p(3) = 3³+ a.3²+ b.3 +6= 27+9a +3b +6 =33+9a+3b = 3

11+3a +b =1

3a+b =-10

b=-10-3a→.(ii)

Equating the value of b from (ii) and (i) , we have

(- 7 -2a) = (-10 - 3a)

a = -3

Substituting a = -3 in (i), we get

b = - 7 -2(-3) = -7 + 6 = -1

Thus the values of a and b are -3 and -1 respectively.


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