CBSE Class 10 Answered
how many terms of the AP24,20,16 must be taken so that the sum maybe 72?
Asked by riyaliz | 22 Jul, 2008, 10:42: PM
Expert Answer
first term =24 , common difference = --4
Sn = n / 2 { 2a + (n-1)d } = 72
n / 2 { 2 x24 + (n - 1) x-4} = 72
n { 48 -4n +4 } = 72x2 = 144
n(52 - 4n } = 144 ===> 4n^2 - 52n + 144 = 0
n^2 - 13n +36 = 0 ===> n = -9 , -4 { number of terms should be positive so n = 9 , 4}
no of terms is equal to 9 & 4
Answered by | 23 Jul, 2008, 03:43: PM
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