Question

factorise
(A) x^2+5x-84
(B) 81-16x^2
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Answer 1

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Answer 2

Answer:

Ans A.

Let's factor x2+5x−84

x2+5x−84

The middle number is 5 and the last number is -84.

Factoring means we want something like

(x+_)(x+_)

Which numbers go in the blanks?

We need two numbers that...

• Add together to get 5

• Multiply together to get -84

Can you think of the two numbers?

• Try -7 and 12:

        -7+12 = 5

        -7x12 = -84

• Fill in the blanks in

         (x+_)(x+_)

• with -7 and 12 to get...

        (x-7)(x+12)

Ans B.

Factor 81−16x2

= −16x2+81

=(4x+9)(−4x+9)