Question

Simplify 3x (4x – 5) + 3 and find its values for (i) x = 3 (ii) x =

1

2

.​

Answer 1

3x (4x − 5) + 3 = 12x2 − 15x + 3 (i) For x = 3, 12x2 − 15x + 3 = 12 (3)2 − 15(3) + 3 = 108 − 45 + 3 = 66 (ii) For

ii)x=1/2

3x(4x - 5) + 3

⇒ 3 × \bf \frac{1}{2}

2

1

(4 × \bf \frac{1}{2}

2

1

- 5) + 3 [pu the value of x = \bf \frac{1}{2}

2

1

⇒ \bf \frac{3}{2}

2

3

(2 - 5) + 3

⇒ \bf \frac{3}{2}

2

3

(-3) + 3

⇒ \bf \frac{-9}{2}

2

−9

+ 3

⇒ \bf \frac{-9 + 6}{2}

2

−9+6

⇒ \bf \frac{-3}{2}

2

−3

Answer 2

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3x(4x−5)+3=12x^2−15x+3

x=3 gives the value 12(9)−15×3+3

                             =108−45+3

                              =66

x=1/2 gives the value 12(1/4)−15×(1/2)+3

                             =3−7.5+3

                              = - 3/2