Question

if (x-1) is a factor of polynomial 3x2+2x-k

Answer 1

zero of x-1 is 1.
so, p(x)=3x^2+2x-k
=>p(1)=3(1)^2+2(1)-k=0
=>p(1)=3+2-k=0
=>p(1)=5-k=0
so, 5-k=0
=>-k=-5
=>k=5

Answer 2

Heya user, Here is your answer
$given \: that \: (x - 1) \: is \: the \: factor \: of \: 3 {x}^{2} + 2x - k \\ so \: zero \: of \: x - 1 = 1 \\ therefore \: \\ p(1) = 0 \\ 3( {1)}^{2} + 2(1) - k = 0 \\ 3 + 2 - k = 0 \\ 5 - k = 0 \\ k = 5$
Hope it will help you