Factorize
`(i) ab+bc +ax +cx`
`(ii) x^2+3x+x+3`
`(iii) 6ab-b^2+12ac-2bc`
`(iv) a^2-b-ab -a`

Explanation

We have
`(i) ab+bc +ax +cx =(ab+bc)+(ax+cx)`
`=b(a+c)+x(a+c)=(a+c)b+x)`.
`(ii) x^2+3x+x+3=(x^2+3x)+(x+3)`
` x(x+3)+(x+3)=(x+3)(x+1)`
`(iii) 6ab-b^2+12ac-2bc=(6ab+12ac)-(b^2+2bc)`
`= 6a(b+2c)-b(b+2c)`
` =(b+2c)(6a-b)`
`(iv) a^2+b-ab-a=a^2-a-ab+b=(a^2-a)-(ab-b)`
` =a(a-1)-b(a-1)=(a-1)(a-b)`.