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Question

Simplify each of the following as a single polynomial.

(i) (3x + 3) (3x + 2)

(ii) (3x − 4) (4x − 3)

(iii)

(iv)

(v)

(vi)

(vii)


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Solution

(i)

(3x + 3)(3x + 2)

= (3x × 3x) + (3x × 2) + (3 × 3x) + (3 × 2)

= 9x2 + 6x + 9x + 6

= 9x2 + (6 + 9)x + 6

= 9x2 + 15x + 6


(ii)

(3x 4) (4x 3)

= (3x × 4x) (3x × 3) (4 × 4x) + (4 × 3)

= 12x2 9x 16x + 12

= 12x2 (9 + 16)x + 12

= 12x2 25x + 12


(iii)

(2x − 3) (4x2 + 6x + 9)

= (2x × 4x2) + (2x × 6x) + (2x × 9) (3 × 4x2) (3 × 6x) (3 × 9)

= 8x3 + 12x2 + 18x12x218x − 27

= 8x3 + (12 − 12)x2 + (18 − 18)x − 27

= 8x3 − 27


(iv)

(2x + 3) (4x26x + 9)

= (2x × 4x2) − (2x × 6x) + (2x × 9) + (3 × 4x2) (3 × 6x) + (3 × 9)

= 8x312x2 + 18x + 12x218x + 27

= 8x3 + (−12 + 12)x2 + (18 − 18)x + 27

= 8x3 + 27


(v)

(x − 1)(x2 + x + 1)

= (x × x2) + (x × x) + (x × 1) − (1 × x2) − (1 × x) − (1 × 1)

= x3 + x2 + xx2x − 1

= x3 + (1 − 1)x2 + (1 − 1)x − 1

= x3 − 1


(vi)

(x + 1)(x2x + 1)

= (x × x2) − (x × x) + (x × 1) + (1 × x2) − (1 × x) + (1 × 1)

= x3x2 + x + x2x + 1

= x3 + (−1 + 1)x2 + (1 − 1)x + 1

= x3 + 1


(vii)

(2x + 2)(5x + 4) − (2x + 3)(4x + 5)

= (2x × 5x) + (2x × 4) + (2 × 5x) + (2 × 4) − (2x × 4x) − (2x × 5) − (3 × 4x) − (3 × 5)

= 10x2 + 8x + 10x + 8 − 8x2 − 10x − 12x − 15

= (10 − 8)x2 + (8 + 10 − 10 − 12)x + (8 − 15)

= 2x2 − 4x − 7



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