I-Lrn Help dealing with functions

[lcclean]

I'm in need of some help with three different questions. I have tried 3 different times to solve these problems and came up empty.

1) The equation x=(y+8)(y-9) does not express y as a function of x because a unique value of y is not always uniquely determined by a particular value of x. In particular, when x=-60, y can be ____ or ____.
Correct answer is -3,4

2) g(y)=9y squared - 7y + 3; when g(-2)...I came up with 49, correct answer is 53.

3) Consider the function f(x)=(x-7)(x+4). Two values of x for which f(x)=-18 are ____ and ____.
Correct answer is 5,-2

These quizzes are worth 2 extra points on the next test and I need all the points I can get at this time. Your help is greatly appreciated!!!!!!

 

[tkhunny]

I'm in need of some help with three different questions. I have tried 3 different times to solve these problems and came up empty.

Unfortunately, you did not tell us what you did during those three attempts. This makes it very difficult to assist you. You don't get extra points for me working the problem, do you?

1) The equation x=(y+8)(y-9) does not express y as a function of x because a unique value of y is not always uniquely determined by a particular value of x. In particular, when x=-60, y can be ____ or ____.

Substitute

-60 = (y+8)*(y-9) = y² - y - 72
0 = y² - y - 12

Can you factor that right-hand side?

 

[galactus]

I'm in need of some help with three different questions. I have tried 3 different times to solve these problems and came up empty.

1) The equation x=(y+8)(y-9) does not express y as a function of x because a unique value of y is not always uniquely determined by a particular value of x. In particular, when x=-60, y can be ____ or ____.
Correct answer is -3,4A quadratic, y²-y-72=-60, solve for y.

2) g(y)=9y squared - 7y + 3; when g(-2)...I came up with 49, correct answer is 53. Just enter -2 in for y. If you came up with 49 you had better try again.

3) Consider the function f(x)=(x-7)(x+4). Two values of x for which f(x)=-18 are ____ and ____.
Correct answer is 5,-2
This is just a quadratic equation. x²-3x-28=-18, solve for x.

These quizzes are worth 2 extra points on the next test and I need all the points I can get at this time. Your help is greatly appreciated!!!!!!

 

[lcclean]

First, thank you very much for the help. I'm still having a problem with question #2.

g(y)=9y squared-7y+3 when g(-2)

I come up with :
9(-2) squared - 7(-2) +3
9*(-4) - (-14) +3
-36 +14 +3
-19

I'm sure its just simple math but I'm getting confused. Even when I put it in my TI-83 its still coming up wrong.

 

[lcclean]

I just wanted to show you I figured it out...

x=(y+8)(y-9)
-60=y squared -y-72
-60+60=y squared -y-72+60
0=y squared -y-12
(y-4)(y+3)=0
y-4=0 y+3=0
+4 =+4 -3=-3
y=4 y =-3


f(x)=(x-7)(x+4)
-18=x squared - 3x-28
-18+18=x squared -3x -28 +18
0=x squared -3x -10
0=(x-5)(x+2)
x-5=0 x+2=0
+5=+5 -2=-2
x=5 x=-2

Thanks again

 

[Denis]

9(-2) squared - 7(-2) +3
9*(-4) - (-14) +3 : NO: (-2) squared = 4, not -4