Answer:
Tn = -n^2 - n + 21 is the formula for the nth term.
Step-by-step explanation:
The second differences are all equal in this quadratic sequence.
Now, the quadratic sequence has a formula of Tn = an^2 + bn + c
Find the value of a in an^2 by dividing the difference by 2:
-2/2 = -1
a = -1
Since T1 is 19 and T2 is 15 we can put that into the equation and simplify:
b + c = 20
2b + c = 19
Thus, b = -1 , c = 19 and the general formula for the nth term is Tn = -n^2 - n + 21
The answer is 40.
Because when you multiply 2 numbers, it becomes a positive number.(-4x10 or -2x3)
But if it were only one negative and positive then it would be negative because the answer is negative when you multiply by one negative number.
8x-10y=-23
9x+10y=-16
(8x+9x)+(10y-10y)=(-23+(-16))
17x+0y=-39
x=-39/17
8(-39/17)-10y=-23
-312/17-10y=-23
-10y=-23+312/17
-10y=-79/17
y=79/170
