Question

if 2a-3b =3 and ab=2,find the value of 2a*2a*2a-3b*3b*3b

Answer 1

=(a2+b2)-(a-b)2

=(a2+b2)-(a2-2ab+b2)

removing brackets

=a2+b2-a2+2ab-b2

hence we get 2ab

therefore 

2ab=(a2+b2)-(a-b)2

they have given the value of a2+b2=29 and a-b=3. substituting the value

2ab= 29-(3)2 

=29-3*3

=29-9

2ab=20

ab=20/2

ab=10 

I think you got me.. have a nice day..