Is there formal proof for (-)(-)= (+). Please help me to get the answer. This, has been ask by my Maths teacher in school.
A expert answered this, but, he told me that how (-1) x (-1) = 1. Actually, it has some expressions like "-(-1) = 1.
Here we have (-)(-).. without proof.
So, please be a little specific.
Hi,
First of all the axioms does not require proof because they are self evidently true.
and the previous answer:
From the distributive law of multiplication we have
a*(b+c) = a*b + a*c
which holds for all real numbers. So it will hold if we put a=-1, b=1 and c=-1
(-1)*(1+(-1)) = (-1)*1 + (-1)*(-1)
1+(-1) = 0 and -1*1 = -1 so we get
(-1)*0 = -1 + (-1)*(-1)
0 = -1 + (-1)*(-1)
rearrange to get
1 = (-1)*(-1)
It is correct and also
The above explanation has nowhere "-(-1) " so it is the required proof.