Asked by FEBIN
                the sum of the n termsof an ap whose first term is 5 and common difference is 36 is equal to the sum of 2n terms of another AP whose first term is 36 ans common difference is 5. Find n?
            
            
        Answers
                    Answered by
            Reiny
            
    sum of n terms of 1st = (n/2)(10 + 36(n-1))
= (n/2)(36n - 26)
sum of 2n terms of 2nd = (2n/2)(72 + 5(2n-1))
= n(10n + 67)
(n/2)(36n - 26) = n(10n + 67)
divide by n, and multiply by 2
36n - 26 = 20n + 134
16n = 160
n = 10
check:
sum(10 for 1st) = 5(10 + 36(9)) = 1670
sum(20 for 2nd) = 10(72 + 19(5)) = 1670
all is good!
    
= (n/2)(36n - 26)
sum of 2n terms of 2nd = (2n/2)(72 + 5(2n-1))
= n(10n + 67)
(n/2)(36n - 26) = n(10n + 67)
divide by n, and multiply by 2
36n - 26 = 20n + 134
16n = 160
n = 10
check:
sum(10 for 1st) = 5(10 + 36(9)) = 1670
sum(20 for 2nd) = 10(72 + 19(5)) = 1670
all is good!
                    Answered by
            ravi
            
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                    Answered by
            ravi
            
    All well
    
                    Answered by
            Prince Sharma
            
    Nice it's clear my doubts
    
                    Answered by
            deepthi
            
    nice cleared my doubt 
    
                    Answered by
            Sahil
            
     Chutiya hai tuu
    
                    Answered by
            siddharth
            
    nice one mathematician
    
                    Answered by
            Anonymous
            
    thanks 
    
                    Answered by
            MANYA
            
    really helped........thanks
    
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