If r=xi+y j+zk |bar( r)|=r then show that grad((1)/(r))=(-bar(r))/(r^(2))​

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1. Let the C P of the toy = Rs.100

   If the gain is 12%, the first S P = 100 + 12 = Rs.112

   If he had been sold Rs.33 more gain = 14 %

   Therefore second S P = 100 = 14 = Rs 114 .

   Difference in second S P and first S P = Rs.2 [ 114 – 112=2]

   If Rs,2 is the difference in S P , cost price = Rs. 100

   If the difference in S P is Rs.33, cost price = 100/2*33= 50 x 33 = Rs1650

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