Question

in AP the fourth and sixth term are 8 and 14 respectevily find the first term and common difference and sum of the first 20 terms

Answer 1

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Answer 2

Answer

Fourth term = a+ 3d =8........1

Sixth term = a+5d =14..........2

Using elimination method in eq 1 and 2

so => -2d = -6

=> d = 3

hence putting d =3 in eq 1

a + 3X3 =8

a =-1

Sn = n/2 (2a +(n-1)d)

S20 =20/2 (2x-1+(20-1)3)

= 10(-2+57)

S20 =550