(a + b - c)(a + b + c)

I kind of understand the box method but it's not coming out right and I'm not sure where I went wrong. Please help;(

Question

(a + b - c)(a + b + c)

I kind of understand the box method but it's not coming out right and I'm not sure where I went wrong. Please help;(

runner01 · Answer

b

mathmale · Answer

Welcome to OpenStudy!!

Regarding (a + b - c)(a + b + c):

Review "special products and factors."  One such special product is$$(x-a)(x+a)=x^2-a^2$$

mathmale · Answer

Rewrite your  (a + b - c)(a + b + c)    as  ([a + b] - c)([a + b] + c) and then replace each [a+b] with d:  (d+b)(d-b).  Try this multiplication.  

Then, when done, substitute back into your result [a+b0 for each occurrence of d.

runner01 · Answer

b2 but it can be 34

mathmale · Answer

@runner01:  Kindly help others by sharing methods and giving guidance, and do NOT provide direct answers.  The other person needs to be involved in finding the solution.

runner01 · Answer

ok sorry i forgot to put the way i sovled it

woodsymte · Answer

Ok but where did you get (d+b)? I understand subbing the a+b but where the b on the ends come from?