Answer:
general rule Un=1.8n-21
U100=1.8(100)-21=159
Step-by-step explanation:
a5=a+4d, a5=-12
a10=a+9d, a10=-3
-12=a+4d
-3=a+9d subtract the system of equations
-9=-5d solve for d
d=1.8
substitute d into first equation to find a
-12=a+4(1.8)
a=-19.2
un. = a + (n − 1)d
Un=-19.2+(n-1)(1.8)
Un=1.8n-21
