SOLUTION: Hi, Please can any one help with the following? Many thanks. Hugh Factorise the following expressions. (i) x^2 − x − 42 (ii) 9m^2 − 81n^2

Algebra ->  Equations -> SOLUTION: Hi, Please can any one help with the following? Many thanks. Hugh Factorise the following expressions. (i) x^2 − x − 42 (ii) 9m^2 − 81n^2      Log On


   

Question 836155: Hi,
Please can any one help with the following? Many thanks. Hugh
Factorise the following expressions.
(i) x^2 − x − 42
(ii) 9m^2 − 81n^2
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
(ii) is the difference of squares. %283m%2B9n%29%283m-9n%29

(i) Look for factors of 42 which could be arranged as sum or difference to give -1. Obvious choice is 6 and 7, but which signs? For the -42, one be negative and other be positive. For the -x, you want 6-7:
%28x%2B6%29%28x-7%29