1.

Find the 20th term of the series 2 x 4 + 4 x 6 + 6 x 8 +……….. + n terms.

Answer»

We have Tn = a + (n – 1)d 

20th term of series 

= [20th term of 2,4, 6….] x [20th term of 4, 6, 8….. ] 

= [2 + (20 -1)2] x [4+ (20-1)2

= (2+ 38)(4 + 38) 

= (40)(42) = 1680



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