Question

Simplify 3x (4x-5)+3 and find its value fo (i) x=3 (ii)x=1/2

Answer 1

$x = 3 \\ 3x(4x - 5) + 3 \\ 3 \times 3(4 \times 3 - 5) + 3 \\ 9(12 - 5) + 3 \\ 9 \times 7 + 3 \\ 63 + 3 \\ 66$
$x = \frac{1}{2} \\ 3 \times \frac{1}{2} (4 \times \frac{1}{2} - 5) + 3 \\ \frac{3}{2} ( \frac{4}{2} - 5) + 3 \\ \frac{3}{2} ( \frac{4 - 10}{2} ) + 3 \\ \frac{3}{2} \times \frac{ - 6}{2} + 3 \\ \frac{ - 18}{4} + \frac{3}{1} \\ \frac{ - 18 + 12}{4} = \frac{ - 6}{4} = \frac{ - 3}{2}$

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