Factorise
(i) `x^(2)+9x+18` `" "`(ii) `6x^(2)+7x-3`
(iii) `2x^(2)-7x-15 `` " " `(iv)` 84-2r-2r^(2)`

Explanation

(i) `x^(2)+9x+18=x^(2)+6x+3x+18` {by splitting middle term]
`=x(x+6)+3(x+6)=(x+3)(x+6)`
(ii) `6x^(2)+7x-3=6x^(2)+9x-2x-3` [by splitting middle term]

`=3x(2x+3)-1(2x+3)` `=(3x-1)(2x+3)`


(iii) `2x^(2) -7x -15=2x^(2) -10x+3x-15` [by splitting middle term]
` =2x(x-5)+3(x-5)=(2x+3)(x-5)`
(iv) ` 84-2r-2r^(2)=-2(r^(2)+r-42)`
`=-2(r^(2)+7r-6r-42)` [by splitting middle term]
`=-2[r(r+7)-6(r+7)]`
`=-2(r-6)(r+7)=2(6-r)(r+7)`