The first term of an A.P. is -5 and the 6th term is 45 . Find S6
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Answer => S6 = 120
Let a = -5
a6 = 45
S6 = ?
=> an = a + (n-1)d
=> a6 = -5 + (6-1)d
=> 45= -5 + 5d
=> 45+5 = 5d
=> 50 = 5d
=> d = 10
Sn = n/2( 2a + (n-1)d )
S6= 6/2( 2 x -5 + (6-1)10 )
S6 = 120
Let a = -5
a6 = 45
S6 = ?
=> an = a + (n-1)d
=> a6 = -5 + (6-1)d
=> 45= -5 + 5d
=> 45+5 = 5d
=> 50 = 5d
=> d = 10
Sn = n/2( 2a + (n-1)d )
S6= 6/2( 2 x -5 + (6-1)10 )
S6 = 120
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