What is that least digit that must be added to the product 5786 × 5784 to make it a perfect square?
Expression : 5786 × 5784
= $$(5785+1)\times(5785-1)$$
Let $$5785=x$$
=> $$(x+1)(x-1)=x^2-1$$
Clearly to make above term a perfect square, we need to add 1
=> $$x^2-1+1=x^2$$
=> Ans - (A)
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