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Mathematics

Using remainder theorem, find the remainder when:

f(x) = 9x2 - 6x + 2 is divided by (3x - 2).

Factorisation

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Answer

By remainder theorem,

If f(x) is divided by (x - a), then remainder = f(a).

f(x) = 9x2 - 6x + 2

Divisor :

⇒ (3x - 2) = 0

⇒ 3x = 2

⇒ x = 23\dfrac{2}{3}

Substituting x = 23\dfrac{2}{3} in f(x), we get :

f(23)=9(23)26(23)+2=9(49)6(23)+2=44+2=2.\Rightarrow f\Big(\dfrac{2}{3}\Big) = 9\Big(\dfrac{2}{3}\Big)^2 - 6\Big(\dfrac{2}{3}\Big) + 2 \\[1em] = 9\Big(\dfrac{4}{9}\Big) - 6\Big(\dfrac{2}{3}\Big) + 2 \\[1em] = 4 - 4 + 2 \\[1em] = 2.

Hence, remainder = 2.

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