4xy - 7y + 2x is -169 when x=-4 & y=7

[Zoro.]

I am completely new to Pre-Algebra stuff so any help will be greatly appreciated.
I know how to get the 3 sets of numbers but not sure how to get to the single value correctly.

I have 3 sample problems
1st sample:
When x= -4 & y= 7
4xy-7y+2x
4(-4)(7) - 7(7) + 2(-4)
(-112) - (-49) + (-8)
= -169
Why are all 3 numbers added?

2nd sample:
When x=7 & y= -4
4xy - 7y + 2x
4(7)(-4) - 7)-4) + 2(7)
(-112) - (-28) + (14)
= -70
Why are these all subtracted?

3rd sample:
When x=2 & y= -4

4x + 7yx - 2x ......................................edited
4(2) + 7(-4)(2) - 2(2)
(8) + (-56) - (4)
= -52
Why are some added and subtracted?

What makes these 3 different on the way it is solved?

Thanks

 

[stapel]

I am completely new to Pre-Algebra stuff so any help will be greatly appreciated.
I know how to get the 3 sets of numbers but not sure how to get to the single value correctly.

I have 3 sample problems
1st sample:
When x= -4 & y= 7
4xy-7y+2x
4(-4)(7) - 7(7) + 2(-4)
(-112) - (-49) + (-8)
= -169
Why are all 3 numbers added?

One of the signs is a "minus" and the next is a "plus". Once the double negative in the middle is simplified, you'll have:

. . . . .-112 + 49 + (-8)

Is this what you mean by "all 3 numbers added"? If you're not sure about how to simplify with "minus" signs, try here.

2nd sample:
When x=7 & y= -4
4xy - 7y + 2x
4(7)(-4) - 7)-4) + 2(7)
(-112) - (-28) + (14)
= -70
Why are these all subtracted?

One of the signs in between numbers is a "minus", while the other is a "plus". Once the subtraction of a negative is simplified, you'll have:

. . . . .-112 + 28 + 14

What do you mean by "all subtracted"?

3rd sample:
When x=2 & y= -4

4x + 7yx - 2x ......................................edited
4(2) + 7(-4)(2) - 2(2)
(8) + (-56) - (4)
= -52
Why are some added and subtracted?

What makes these 3 different on the way it is solved?

They're all applying the same rules in the same ways. In what manner are you seeing these as being "different" in how they're simplified?

Please be complete. Thank you!

 

[Steven G]

I am completely new to Pre-Algebra stuff so any help will be greatly appreciated.
I know how to get the 3 sets of numbers but not sure how to get to the single value correctly.

I have 3 sample problems
1st sample:
When x= -4 & y= 7
4xy-7y+2x
4(-4)(7) - 7(7) + 2(-4)
(-112) - (-49) + (-8)=(-112)+ (49) - (8) = -63 -8 = -71, NOT -169
= -169
Why are all 3 numbers added?

2nd sample:
When x=7 & y= -4
4xy - 7y + 2x
4(7)(-4) - 7)-4) + 2(7)
(-112) - (-28) + (14)
= -70
Why are these all subtracted?

3rd sample:
When x=2 & y= -4

4x + 7yx - 2x ......................................edited
4(2) + 7(-4)(2) - 2(2)
(8) + (-56) - (4)
= -52
Why are some added and subtracted?

What makes these 3 different on the way it is solved?

Thanks

Please see red above.