Maths!!!

Let u = 2(3y + 7)



[2(3y + 7) + 1] [2(3y + 7) - 1]

= [u + 1] [u - 1]

= u2 - 1

= [2(3y + 7)]2 - 1

= (6y + 14)2 - 1

= [(6y)2 + 2(6y)(14) + (14)2] - 1

= [36y2 + 168y + 196] - 1

= 36y2 + 168y + 195
=

[ 2(3y+7)+1 ] [ 2(3y+7)-1 ]
=[(6y+14)+1] [(6y+14)-1]
=(6y+15) (6y+13)
=36y2+78y+90y+195
=36y2+168y+195
-----------------------------------------------------------
you can also calculate this equation by using one of the indentities,(a+b)(a-b)=(a2-b2)
[ 2(3y+7)+1 ] [ 2(3y+7)-1 ]
=[(6y+14)2-12]
=(36y2+84y+84y+196)-1
=(36y2+168y+196)-1
=36y2+168y+196-1
=36y2+168y+195

[ 2(3y+7)+1 ] [ 2(3y+7)-1 ]
=[2(3y+7)]^2 -1^2
=[6y+14]^2 -1
=36y^2+168y+196-1
=36y^2+168y+195


=================================================

奇實喱個就好似一條idenity啲公式: (A+B)(A-B)
你把2(3y+7)係A, 1係B..
咁你就會識計..





p.s.我唔知有冇計錯數- -

ans. (6y+15)(6y+13)