If `x_1, x_2, x_3,...... x 2_n` are in `A.P`, then `sum _(r=1)^(2n) (-1)^(r+1) x_r^2` is equal to

If x_1, x_2, x_3,...... x _(2n) are in A.P , then sum _(r=1)^(2n) (-1)^(r+1) x_r^2 is equal to (a) (n)/((2n-1))(x _(1)^(2) -x _(2n) ^(2)) (b) (2n)/((2n-1))(x _(1)^(2) -x _(2n) ^(2)) (c) (n)/((n-1))(x _(1)^(2) -x _(2n) ^(2)) (d) (n)/((2n+1))(x _(1)^(2) -x _(2n) ^(2))

If x_(1),x_(2),x_(3),......x2_(n) are in A.P, then sum_(r=1)^(2n)(-1)^(r+1)x_(r)^(2) is equal to

Q. if x_1,x_2......x_n are in H.P ., then sum_(r=1)^n x_r x_(r+1) is equal to : (A) (n-1)x_1 x_n (B) n x_1 x_n (C) (n+1)x_1 x_n (D) (n+2)x_1 x_n

lim_(x to oo ) tan { sum_(r=1)^(n) tan^(-1) ((1)/( 1 +r +r^2))} is equal to ________.

Let f (x ) = | 3 - | 2- | x- 1 |||, AA x in R be not differentiable at x _ 1 , x _ 2 , x _ 3, ….x_ n , then sum _ (i= 1 ) ^( n ) x _ i^2 equal to :

Let f (x ) = | 3 - | 2- | x- 1 |||, AA x in R be not differentiable at x _ 1 , x _ 2 , x _ 3, ….x_ n , then sum _ (i= 1 ) ^( n ) x _ i^2 equal to :

If x+y=1 , then sum_(r=0)^(n)r^(2)""^(n)C_(r)x^(r)y^(n-r) equals:

lim_(xrarr2)(sum_(r=1)^(n)x^r-sum_(r=1)^(n)2r)/(x-2) is equal to