Find the mean and standard deviation of first n terms of an A.P. whose first term is a and common difference is d.

Explanation

`((x),(a),(a+d),(a+2d),(....),(a+(n-1)d))`
`((x-a),(0),(d),(2d),(....),((n-1)d))`
`(((x-a)^2),(0),(d^2),(....),(4d^2),((n-1)^2d^2))`

Mean`=1/n[n/2(2a+(n-1)d)]
=a+(n-1)/d`

`sum(x-a)=d[1+2+3+...+(n-1)d]
=d(n(n-1)/2)`


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