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Q.

Evaluate the following by using the identities:-

28 $\times$ 32

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a

869

b

896

c

894

d

899

answer is B.

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Detailed Solution

Concept: First we need to look at which identity we can use and then we have converted the two numbers such that both become equal i.e. 30 and solved using the identity a2-b2.
28

\times

32
Now we will convert 28 and 32 such that both become equal i.e for 28 we will have 30-2 and for 32 we will have 30+2.
=(30-2) (30+2) . ….(a-b ) (a+b )
Now we will solve it using identity a2-b2.
=(30 ) 2-(2) 2. ….(a ) 2-(b ) 2
=900-4
=896.
Hence, the correct option is (2) .

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