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if (2x^3 + ax^2+bx-2) when divided by (2x-3) and (x+3) leaves remainder 7 and -20 respectively, find the values of a and b

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if (2x^3 + ax^2+bx-2) when divided by (2x-3) and (x+3) leaves remainder 7 and -20 respectively-example-1
if (2x^3 + ax^2+bx-2) when divided by (2x-3) and (x+3) leaves remainder 7 and -20 respectively-example-2
User Stuart Marks
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Answer:

  • a = 3
  • b = -3

Explanation:

The remainder from division by (2x-3) is the same as the value of the function when that divisor is zero—at x = 3/2.

((2(3/2) +a)(3/2) +b)(3/2) -2 = 7

((3 +a)(3/2) +b)(3/2) = 9 . . . . add 2

9/2 +3/2a + b = 6 . . . . . . . . multiply by 2/3

3/2a +b = 3/2 . . . . . . . . . . . subtract 9/2

3a +2b = 3 . . . . . . . . . . . . . multiply by 2 [eq1]

The remainder from division by (x+3) is the same as the value of the function for x = -3.

((2(-3) +a)(-3) +b)(-3) -2 = -20

(-6 +a)(-3) +b = 6 . . . . . . add 2 and divide by -3

18 -3a +b = 6 . . . . . . . . . eliminate parentheses

3a -b = 12 . . . . . . . . . . . subtract 18, multiply by -1 [eq2]

Subtracting the [eq2] from [eq1], we have ...

(3a +2b) -(3a -b) = (3) - (12)

3b = -9 . . . . . simplify

b = -3 . . . . . . divide by 3

From [eq2], ...

3a -(-3) = 12 . . . . substitute for b

3a = 9 . . . . . . . . subtract 3

a = 3 . . . . . . . . . divide by 3

The values of 'a' and 'b' are 3 and -3, respectively.

if (2x^3 + ax^2+bx-2) when divided by (2x-3) and (x+3) leaves remainder 7 and -20 respectively-example-1
User Suslik
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