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Let p (x) = 3x3 + x2 - 22x + 9 and q (x) = 3x2 + 7x - 6. By division algorithm, When p (x) is divided by q (x), the remainder is a linear expression in x. So, let r (x) = ax + b is added to p (x) so that p (x) + r (x) is divisible by q (x). Let, f (x) = p (x) + r (x) = 3x3 + x2 – 22x + 9 + (ax + b) = 3x3 + x2 + x (a – 22) + b + 9 We have, q (x) = 3x2 + 7x – 6 q (x) = 3x (x + 3) – 2 (x + 3) q (x) = (3x – 2) (x + 3) Clearly, q (x) is divisible by (3x – 2) and (x + 3). i.e. (3x – 2) and (x + 3) are factors of q(x), Therefore, f(x) will be divisible by q(x), if (3x – 2) and (x + 3) are factors of f(x). i.e. f (2/3) = 0 and f (-3) = 0 [∵ 3x – 2 = 0, x = 2/3 and x + 3 = 0, x = -3] f (2/3) = 0
⇒ 6a + 9b – 39 = 0 ⇒ 3 (2a + 3b – 13) = 0 ⇒ 2a + 3b – 13 = 0 (i) Similarly, f (-3) = 0 ⇒ 3 (-3)3 + (-3)2 + (-3) (a – 2x) + b + 9 = 0 ⇒ -81 + 9 – 3a + 66 + b + 9 = 0 ⇒ b – 3a + 3 = 0 ⇒ 3 (b – 3a + 3) = 0 ⇒ 3b – 9a + 9 = 0 (ii) Subtract (i) from (ii), we get 3b – 9a + 9 – (2a + 3b – 13) = 0 3b – 9a + 9 – 2a – 3b + 13 = 0 ⇒ -11a + 22 = 0 ⇒ a = 2 Putting value of a in (i), we get ⇒ b = 3 Putting the values of a and b in r (x) = ax + b, we get r (x) = 2x + 3 Hence, p (x) is divisible by q (x) if r (x) = 2x + 3 is divisible by it. By division algorithm, when p(x) = 3x3 + x2 − 22x + 9 is divided by `3x^2 + 7x - 6,`the reminder is a linear polynomial. So, let r(x) = ax + b be added to p(x) so that the result is divisible by q(x) Let `f(x) = p(x) + r(x)` ` = 3x^2 + x^2 - 22x + 9 ax +b` ` = 3x^2 + x^2 +(a- 22) x + 9 + b` We have \[q\left( x \right) = 3 x^2 + 7x - 6\] \[ = 3 x^2 + 9x - 2x - 6\] \[ = 3x\left( x + 3 \right) - 2\left( x + 3 \right)\] \[ = \left( 3x - 2 \right) \left( x + 3 \right)\] Clearly,
\[\left( 3x - 2 \right)\] and \[\left( x + 3 \right)\]
are factors of q(x). Therefore, f(x) will be divisible by q(x) if (3x - 2)and (x + 3)are factors of f(x), i.e., `f (2/3)`and f(−3) are equal to zero. Now, \[f\left( \frac{2}{3} \right) = 0\] \[ \Rightarrow 3 \left( \frac{2}{3} \right)^3 + \left( \frac{2}{3} \right)^2 + \left( a - 22 \right)\left( \frac{2}{3} \right) + 9 + b = 0\] \[ \Rightarrow 3 \times \frac{8}{27} + \frac{4}{9} + \frac{2a}{3} - \frac{44}{3} + 9 + b = 0\] \[ \Rightarrow \frac{8}{9} + \frac{4}{9} - \frac{44}{3} + 9 + \frac{2a}{3} + b = 0\] \[ \Rightarrow \frac{8 + 4 - 132 + 81}{9} + \frac{2a}{3} + b = 0\] \[ \Rightarrow - \frac{39}{9} + \frac{2a}{3} + b = 0\] \[ \Rightarrow \frac{2a}{3} + b = \frac{13}{3}\] \[ \Rightarrow 2a + 3b = 13 . . . . . . . . \left( i \right)\] And \[f\left( - 3 \right) = 0\] \[ \Rightarrow 3 \left( - 3 \right)^3 + \left( - 3 \right)^2 + \left( a - 22 \right)\left( - 3 \right) + 9 + b = 0\] \[ \Rightarrow - 81 + 9 - 3a + 66 + 9 + b = 0\] \[ \Rightarrow - 3a + b = - 3 \] \[ \Rightarrow b = - 3 + 3a . . . . . . . . . \left( ii \right)\] Substituting the value of b from (ii) in (i), we get, \[2a + 3\left( 3a - 3 \right) = 13\] \[ \Rightarrow 2a + 9a - 9 = 13\] \[ \Rightarrow 11a = 13 + 9\] \[ \Rightarrow 11a = 22\] \[ \Rightarrow a = 2\] Now, from (ii), we get \[b = - 3 + 3\left( 2 \right) = - 3 + 6 = 3\] So, we have a = 2 and b = 3 Hence, p(x) is divisible by q(x), if 2x + 3is added to it. |