# Why is a+b+c = a-a+c? [closed]

Why does $$a+b+c = a-a+c$$? I don't understand. Is it some math property that i didn't know of?

• just susbtitute $b=-a$ Jan 29 at 12:06
• Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
– Community Bot
Jan 29 at 12:11
• Presumably an earlier part of the question told you about $ABC$ Jan 29 at 12:19

Note that we have $$a+b=0$$, so $$b=-a$$. Using that, we have $$a+b+c=a-a+c$$.
In general, $$a+b+c=a-a+c$$ is not true. It is true only if we know $$b=-a$$.
From second inner product : $$\begin {pmatrix} a & b & c \end{pmatrix} . \begin{pmatrix} 1 \\ 1 \\ 0 \end{pmatrix} = a.1+b.1+c.0$$
As the above two vectors are orthogonal then $$a+b=0$$
So substitute $$b=-a$$ in the equation which you mentioned.