Question

please solve fast....​

Answer 1

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

here a=x , d= x+y-x= y and n=n

Sn= n/2 {2x + (n-1)y }

=n/2 {2x+ny-y}

=( n/2 × 2x )+ (n/2×ny) -(n/2×y)

= nx+ n²y/2 - ny/2

= n{ x+ny/2-y/2 }