Find: `sum_(n=1)^oo 0.4^n`

Find: sum_(r=1)^oo 4 (0.5)^r

Find sum_(r=1)^oo 4 (0.5)^r

Find: sum_(r=1)^oo (-1/3)^r

Find: sum_(r=1)^oo (-8) (-1/2)^r

Find sum_(r=1)^oo (-1/3)^r

Find sum_(r=1)^n (2/3)^r

Find sum_(r=1)^oo (-8) (-1/2)^r

let 0ltphiltpi/2 , x=sum_(n=0)^oocos^(2n)phi , y=sum_(n=0)^oosin^(2n)phi and z=sum_(n=0)^oocos^(2n)phisin^(2n)phi then xyz=?

Find sum_(r=1)^n ( 6r^2 + 4r - 3)

Find sum_(r=1)^n (5r^2 + 4r - 3)