Question

Arithmetic progression
I) The sum of 3rd and 7th terms of an AP is 32 and their product is 220.Find the sum of first twenty-one terms of the AP. ( take the value of d positive)
plz help me fast



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Answer 1

Answer:

$3rd \: term \: \: is \: a + 2d \\ 7th \: \:term \: is \: a + 6d \\ so \: the \: sum = 2a + 8d = 32 \: and - - equ1 \\ product \: is \: (a + 2d) \times (a + 6d) = 220. - - equ2 \\ from \: equ1 \: we \: know \: that \: a = 16 - 4d. \\ so \: substituting \: a \: in \: equ2 \: gives \: the \: value \: of \: d = 3.$

the final d value is 3