Question

How do you factor `4 - 2x - 42y + 21xy` by grouping?

Answer 1

(2 - x)(2 - 21y)

Explanation:

group the expression into 'pairs' as follows

[ 4 - 2x ] + [ -42y + 21xy ]

now factor each pair.

2(2 - x ) - 21y(2 - x )

now 'take out' common factor of (2 - x )

`rArr (2 - x )(2 - 21y )`