A sequence u1,u2,u3,… u_1, u_2, u_3, \dots\,u1,u2,u3,… is defined by
u1=cun=2un−1−5,n≥2 \begin{aligned}u_1 &= c \\u_n &= 2u_{n-1} - 5, \quad n \geq 2\end{aligned} u1un=c=2un−1−5,n≥2Find an expression for u2 u_2\,u2 in terms of ccc.
Show that u3=4c−15u_3 = 4c - 15u3=4c−15.
Find ∑r=14ur\sum_{r=1}^4 u_r∑r=14ur in terms of ccc.