If you have an expression (a+b)^2, to expand the formula (a+b)^2=a^2+2(a)(b)+b^2 is used. Expansion of more complex expression also uses the same formula, for example :
(3x+2y+3z)^2
= [3x+(2y+3z)]^2
= (3x)^2 + 2(3x)(2y+3z)+(2y+3z)^2
= 9x^2 + 12xy + 18xz +(2y)^2 +2(2y)(3z) + (3z)^2
= 9x^2 + 12xy + 18xz + 4y^2 + 12yz + 9z^2
= 9x^2 + 4y^2 + 9z^2 +12xy+18xz+12yz
or view the video below :
The above video is suitable for Form 1, Form 2, Form 3, Form 4 and Form 5 for both Mathematics and Add Maths, Malaysia