# Math Help - Evaluating

1. ## Evaluating

$4x^2 + 3$ when x = 5
103

Evaluate 2a - 3 when a = -5
-13

Evaluate -2a + 6b when a = 6 and b = -3
-30
Not sure if it should be -12a + -18b tho

Evaluate (x + 1) 2 - 5 when x = -3
-9

Evaluate c - 3d when c = 1 and d = 1/3

0.1

Or should it be c - 0.9d?

x + x^3 - 4 x^4 when x = 2
-54
Not sure if this should be -54x

5a + 3a^2 when a = -3
12 or 12a?

Find F when c = 15 in the formula F = 9C/5 + 32

F = 59

*mistook it for an almost-identical question in which all that was different was that c = 30

I'm not sure if I should leave the variables in or not.

2. Originally Posted by gfy010
Evaluate $4x^2 + 3$ when x = 5
103 Correct

Evaluate 2a - 3 when a = -5
-13 Correct

Evaluate -2a + 6b when a = 6 and b = -3
-30 Correct

Not sure if it should be -12a + -18b tho No, you're right the first time.

Evaluate $(x + 1)^2 - 5$ when x = -3
-9 Incorrect. Should be -1

Evaluate c - 3d when c - 1 and d = 1/3 Don't understand this one. What does c equal?

0.1

Or should it be c - 0.9d?

x + x^3 - 4 x^4 when x = 2
-54 Correct
Not sure if this should be -54x No

5a + 3a^2 when a = -3

Find F when c = 15 in the formula F = 9C/5 + 32

F = 86 Incorrect. Should be 59

I'm not sure if I should leave the variables in or not.

Hi gfy010,

See my results in red.

3. ah, thanks*

I messed up some of the questions, edited the first post now.

Tho I'm not sure about ( x + 1 ) 2 - 5 when x = -3

Are you sure it's not -3 + 1, then 2 * -2, then -4 - 5?

It's not the parenthesis to the second power (which would be positive 4), it's the parenthesis * positive 2.

4. Originally Posted by gfy010
ah, thanks*

I messed up some of the questions, edited the first post now.

Tho I'm not sure about ( x + 1 ) 2 - 5 when x = -3

Are you sure it's not -3 + 1, then 2 * -2, then -4 - 5?

It's not the parenthesis to the second power (which would be positive 4), it's the parenthesis * positive 2.
I misinterpreted your writings. I assumed since the 2 was on the right side of the parenthesis, you wanted to square the contents.

If you're just multiplying by 2, then your answer is correct. It is -9.

5. Ah, good to know, thanks again.