Question

find the sum of the series 72 + 70 + 68 + dotdotdot + 40​

Answer 1

Answer:

according to AP (Arthmetic Progression) 952

Explanation:

72+70+68+.......................+40

using formula

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

where sn = sum of n terms

n = number of terms

a = first term

d = difference

To find n = ?

An = a + (n-1) d ( formula of An ( last term)

40 = 72+ (n-1) -2

40-72 = (n-1) -2

-32=(n-1) -2

-32/-2 =(n-1)

(n-1) = 16

n = 16+1

n = 17

now by putting value of n in upper formula of Sn

17/2 (2×72 + (17-1) -2 )

17/2 ( 144+16× -2 )

17/2 (144-32 )

17/2×112

17×56

=952