Use the product (a + b)(a - b) = a^2−b^2 to evaluate : (i) 21*19 (ii) 33*27 (iii) 103*97 (iv) 9.8*10.2 (v) 7.7*8.3 (vi) 4.6*5.4

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Mathew Middleton · Accepted Answer

(  i  )  21  ×  19  =  (  20  +  1  )  (  20  −  1  )  =  (  20      )    2    −  (  1      )    2    =  400  −  1  =  399    (  i  i  )  33  ×  27  =  (  30  +  3  )  (  30  −  3  )  =  (  30      )    2    −  (  3      )    2    =  900  −  1  =  891    (  i  i  i  )  103  ×  97  =  (  100  +  3  )  (  100  −  3  )  =  (  100      )    2    −  (  3      )    2    =  10000  −  9  =  9991    (  i  v  )  9.8  ×  10.2  =  (  10  −  .2  )  (  10  −  .2  )  =  (  10      )    2    −  (  .2      )    2    =  100  −  .04  =  99.96    (  v  )  7.7  ×  8.3  =  (  8  −  .3  )  (  8  +  .3  )  =  (  8      )    2    −  (  .3      )    2    =  64  −  .09  =  63.91    (  v  i  )  4.6  ×  5.4  =  (  5  −  .4  )  (  5  +  .4  )  =  (  5      )    2    −  (  .4      )    2    =  25  −  .16  =  24.84

Use the product (a + b)(a - b) = a^2−b^2 to evaluate : (i) 21*19...

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