Answer:
y=5x^2-5x-10
y=2x^2+18x+36
y=-2x^2+2x+40
y=-4x^2-20x-24
Step-by-step explanation:
7, 5, 3, 1 is an arithmetic sequence with common difference (d) = -2 and first term (a) = 7.
Tn = a + (n -1)d
T50 = 7 + (50 - 1) x -2 = 7 + 49 x -2 = 7 - 98 = -91
50th term = -91
I think it’s gonna be 1-log(y). You use the quotient rule of logarithms.
5.
Let x be the age of the father and y be the age of the son. As of today, he's 3 times older, so we have 
10 years ago their ages were, respectively, x-10 and y-10, and the father was 5 times older: 
So, we have the system

Using the first equation, we can substitute every occurrence of "x" with "3y" in the second equation:

So, the son is 20 years old, which means that the father is 60 years old.
Indeed, 10 years ago they were 10 and 50 years old, so the father was 5 times older.
6.
Let x be the age of the grandfather and y the age of the granddaughter. We know that the grandfather is 10 times older: 
He also is 54 years older: 
Again, if we substitute x=10y in the second equation we have
