Factorise $x^{2} - 12 x - 45$ and find its value for $x = 3.$ [3 MARKS]

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Solution

Concept: 1 Mark
Application: 1 Mark
Substitution: 1 Mark

$x^{2} - 12 x - 45$ [ (-15)+3=-12 and (-15)(3)=-45 ]

$= x^{2} - 15 x + 3 x - 45$

$= x (x - 15) + 3 (x - 15)$

$= (x + 3) (x - 15)$

$A t x = 3,$

$(x + 3) (x - 15)$

$= (3 + 3) (3 - 15)$

$= - 72$

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Factorise $x^{2} - 12 x - 45$ and find its value for $x = 3.$ [3 MARKS]

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Factorise x2−12x−45 and find its value for x=3. [3 MARKS]

Concept: 1 Mark Application: 1 Mark Substitution: 1 Mark x2−12x−45 [ (-15)+3=-12 and (-15)(3)=-45 ] =x2−15x+3x−45 =x(x−15)+3(x−15) =(x+3)(x−15) At x=3, (x+3)(x−15) =(3+3)(3−15) =−72

Factorise $x^{2} - 12 x - 45$ and find its value for $x = 3.$ [3 MARKS]

Concept: 1 Mark
Application: 1 Mark
Substitution: 1 Mark

$x^{2} - 12 x - 45$ [ (-15)+3=-12 and (-15)(3)=-45 ]

$= x^{2} - 15 x + 3 x - 45$

$= x (x - 15) + 3 (x - 15)$

$= (x + 3) (x - 15)$

$A t x = 3,$

$(x + 3) (x - 15)$

$= (3 + 3) (3 - 15)$

$= - 72$