Answer:
S=n(n+1) therefore 240=n(n+1), 240=2n +n therefore i have to move all to one place and equate to Zero so that will become quadratic equation 240-2n -n=0 so -n -2n +240=0
-12
Step-by-step explanation:
f(-9) = 2/3(-9) + (-6)
f(-9) = -6 + (-6)
-3-5i