I had asked how (-)(+) = (-) I want a formal proof for this This - Maths - Integers

Question

I had asked how (-)(+) = (-)? I want a formal proof for
this

This question was asked by my maths teacher in school But, When I
showed this, he asked that how corollary 1 is proving, (-)(+) = (-)
He means to say how when 2 different signs are multiplied, how to
say that the value is (-) , Please experts make me understand very
specifically, how, (-)(+) = (-), with a formal proof

Neha Sethi · Accepted Answer

Dear student
Please refer to the easy and clear explanation below in a different
method which will help you in understanding the concept in a better
way

There is no as such special proof for -+=-These are just simply the signs rule which states :1)  a negative  and a positive makes a negative 
Example -3×2=-62) two negatives makes a positive
Example -3×-2=63) a positive and a negative makes a negative
Example 3×-2=-64) two positives makes a positive 
Example 3×2=6So we can conclude that "Two like signs makes a positive sign, two unlike signs makes a negativesign"
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Regards