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If Sn denotes the sum of first n terms of an AP, prove that S30=3(S20- S10)

Posted by Daksh Dhakad 6 years, 10 months ago

CBSE > Class 10 > Mathematics

1 answers

Asmita Joshi 6 years, 10 months ago

S30 = 30/2 ( a+a+29d ) S20 = 20/2 ( a+a+19d ) S10 = 10/2 ( a+a+9d ) S30=3( S20 - S10 ) 15 ( 2a + 29d ) = 3[10(2a + 19d) - 5(2a + 9d)] 30a + 435d = 3[ 20a + 190d - 10a - 45d ] = 3[ 10a + 145d ] = 30a +435d

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