Sum of how many terms of the arithmetic progression 3,7,11.....is 300?
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ajlatha:
your answer is wrong
you can't cancel the 2's like that
we can do it
actually your answer is wrong
just check once
yeah.. sryy
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Answer:
Step-by-step explanation:
3, 7, 11, .....
Sn = 300
n = ?
a = 3
d = 7 - 3 = 4
Sn = 300
n/2 [ 2a + (n - 1) d ] = 300
n [ 2(3) + (n - 1) 4 ] = 600
n [ 6 + 4n - 4 ] = 600
6n + 4n² - 4n = 600
4n² + 2n - 600 = 0
2n² + n - 300 = 0 ( ÷ by 2)
( 2n + 25) ( 2n - 24) = 0
n = 12 ( n can't be negative)
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