how to prove that minus 1 into minus 1 is equal to plus 1. how to prove that -1 into -1= +1

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Today i will tell you that how minus 1

into minus 1 become plus 1.

         Many of you don’t know that how 

                      -1⨯-1= +1.

आज मैं आपको बताऊंगा कि माइनस 1
और माइनस 1 प्लस 1 कैसे बनता है                            आप में से बहुत से लोग यह
नहीं जानते हैं कि कैसे                           -1-1 = +1।

So let’s start,

                     Let we do not know that -1 into -1 is what?  

We are going to see that how -1 into -1 becomes +1

चलिए, शुरू करते हैं,                       हमें यह नहीं पता है कि -1 में -1 क्या है? हम यह देखने जा रहे हैं कि -1 में -1 कैसे +1 हो जाता है
                               

                                    

                                    

                 -1⨯-1 = cosπ x cosπ    [ cosπ = -1]

→         we can right it as[ 2cosπ х cosπ]/2

Further we know  2cosπ х cosπ = cos[a+b] + cos[a-b]

            Using above formula we can write [ 2cosπ х cosπ]/2

 as

                 Cos[π+π] + cos[π -π]/2

          =[ cos2π + cos 0°] /2

           =[ cos 360° + cos 0°]/2

          = [1+1]/2

           = 2/2

        = +1         ………… PROVED

WE PROVED THAT HOW -1 х -1= +1    

                                       

                                                      THANKS…..