If `sum_(n=1)^n u_n =an^2+bn+c, then |(u_1,u_2,u_3),(1,1,1),(7,8,9)|=` (A) 0 (B) `u_1-u_2+u_3` (C) 1 (D) none of these

Find sum_(n=1)^n u_n if u_n=sum_(n=0)^n1/2^n .

If u_n = 2cos n theta then u_1u_n - u_(n-1) is equal to

The circles x^2 + y^2 + 2ux + 2vy = 0 and x^2 + y^2 + 2u_1 x + 2v_1 y = 0 touch each other at (1, 1) if : (A) u + u_1 = v + v_1 (B) u + v = v_1 + u_1 (C) u/u_1 = v/v_1 (D) none of these

4. The solution set of the inequality sinx 3 cosx 0 is U (en 1) 2 (3n +1) (A) (c) U 6n a, (3n 1) 1) (D) none of these

If U_(n)=2cos n theta, then U_(1)U_(n)-U_(n-1) is equal to -