1. Question:15.Evaluate : (i)`(527 xx 527 xx 527 + 183 xx 183 xx 183)/(527 xx 527 - 527 xx 183 xx 183 xx 183)` (ii)`(458 xx 458 xx 458 - 239 xx 239 xx 239)/(458 xx 458 + 458 xx 239 + 239 xx 239)` (iii)`((614 +168)^2-(614-168)^2/614 xx 168)` (iv)`((832+278)^2+(832-278)^2/832 xx 832 + 278 xx 278)` 

    Answer
    Sol.(i) Given Expression =`(527)^3 + (183)^3/(527)^2 - 527 xx 183 + (183)^2`
                                      
                                       =`a^3 + b^3/a^2 - ab + b^2`
                                      
                                       = (a+b) = (527 + 183) =710
    
          (ii) Given Expression =`(458)^3 - (239)^3/(458)^2+458 xx 239 + (239)^2`
                                        
                                        =`(a^3-b^3)/(a^2+ab+b^2)`
                                        
                                       = (a-b) = (458-239) = 219.
        
          (iii) Given Expression =`(a+b)^2-(a-b)^2)/ab`
        
          (iv) Given Expression =`((a+b)^2+(a-b)^2)/(a^2+b^2)`
                                        
                                         =`(2(a^2+b^2)/(a^2+b^2))`=2






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  2. Question:16.Simplify : (i) `1605 xx 160 =?` `(ii) 1398 xx 1398 =?` 

    Answer
    Sol. (i)`1605 xx 1605 = (1605)^2`
                                =`(1600+5)^2`
                                 =`(1600)^2+5^2+2x1600x5`
                                  =2560000+25+16000
                                  =2576025
    
         (ii)1398x1398=`(1398)^2`
                             =`(1400-2)^2`
                             =`(1400)^2+2^2-2x1400x2`
                             =1960000+4-5600
                              =1954404.






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  3. Question:17. Simplify : (i) `896 xx 896 - 204 xx 204 =?` (ii) `57 xx 57 + 43 xx 43 + 2 xx 57 xx 43 =?` (iii) `81 xx 81 + 68 xx 68 - 2 xx 81 xx 68=?` 

    Answer
    Sol. (i) Given Exp.=`(896)^2-(204)^2`
                              
                              =`(896+204)^2(896-204)`
                               
                              =`1100 xx 692`
                               
                              =761200.
           
     (ii) Gieven Exp. =`(57)^2+(43)^2+2 xx 57 xx 43`
                                  
                            =`a^2+b^2+2ab`,where a = 57b=43
                                  
                            =`(a+b)^2`=`(57+43)^2 = (100)^2`
                                  
                            =10000.
          
     (iii)Given exp.=`(81)^2+(68)^2-2xx81xx68`
                              
                         =`a^2+b^2-2ab`,where a=81&b=68
                              
                         =`(a-b)^2`=`(81-68)^2`=`(13)^2`=169.






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  4. Question:18.Evaluate :`(313 xx 313 + 287 xx 287).` 

    Answer
    `(a^2+b^2)=``1/2``[(a+b)^2`+`(a^2-b)^2`]
       
      :. `(313)^2+(287)^2`
             
       =`1/2``[(313+287)^2`+`(313-287)^2`]
             
       =`1/2``[(600)^2`+`(26)^2]`
              
       =`1/2``(360000+676)`
               
       =180338






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  5. Question:2o.What least number must be subtracted from 2000 to get a number exactly divisible by 17? 

    Answer
    On dividing 2000 by 17,we get 11 as remainder.
    :.Required number to be subtracted =11






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