One for combining like terms, and one solving for x

[flora33]

Hello everyone, I'm new to the board! I'm not very good at Algebra, so forgive my stupid questions! I'm taking an online course and it's tough to get questions answered when I need them. So, I've got two questions...
First, combining like terms:
-3x^2+8x-7x^2+9+2x-1x^2+11

My answer:
-3x^2-7x^2-1x^2=-11x^2
8x+2x=10x
9+11=20
=-11x^2+10x-20 is this the correct answer? I have a hard time with addition of negatives sometimes, especially with all the plus signs in the equation!

My next question is, solve for x:
-3(4x+3)-2=7-2x+3
-12x+(-9)-2=10-2x
-12x+(-11)=10-2x
-12x+(-11)+11+2x=10-2x+11+2x
-10x=21
-10x/10=x
21/-10=-2.1
x=-2.1

Do I check my answer by inserting the 2.1 where x is? I tried and I did not get the same answer on both sides of the equation. If someone could show me how to check my answers too, that would be great. Thank you sooo much!

 

[Mrspi]

Hello everyone, I'm new to the board! I'm not very good at Algebra, so forgive my stupid questions! I'm taking an online course and it's tough to get questions answered when I need them. So, I've got two questions...
First, combining like terms:
-3x^2+8x-7x^2+9+2x-1x^2+11

My answer:
-3x^2-7x^2-1x^2=-11x^2
8x+2x=10x
9+11=20
=-11x^2+10x-20 is this the correct answer? I have a hard time with addition of negatives sometimes, especially with all the plus signs in the equation!


My next question is, solve for x:
-3(4x+3)-2=7-2x+3
-12x+(-9)-2=10-2x
-12x+(-11)=10-2x
-12x+(-11)+11+2x=10-2x+11+2x
-10x=21
-10x/10=x
21/-10=-2.1
x=-2.1

Do I check my answer by inserting the 2.1 where x is? I tried and I did not get the same answer on both sides of the equation. If someone could show me how to check my answers too, that would be great. Thank you sooo much!

For the first problem, when you showed your steps for combining the like terms, you got these results: -11x[sup:i7joeju2]2[/sup:i7joeju2], 10x, and 20. All of these are correct. So, why, when you wrote the result as a polynomial, did you change the 20 to -20?

-11x[sup:i7joeju2]2[/sup:i7joeju2] + 10x + 20

would be correct.

For the second problem, you got x = -2.1.

To check your answer, you substitute -2.1 for x in the original equation....it checked for me.

 

[flora33]

For the first problem, when you showed your steps for combining the like terms, you got these results: -11x[sup:1ntsau3z]2[/sup:1ntsau3z], 10x, and 20. All of these are correct. So, why, when you wrote the result as a polynomial, did you change the 20 to -20?

-11x[sup:1ntsau3z]2[/sup:1ntsau3z] + 10x + 20

would be correct.

For the second problem, you got x = -2.1.

To check your answer, you substitute -2.1 for x in the original equation....it checked for me.

Thank you. For the first problem, I am not sure why I put -20. That was an error. For the second problem, I don't think I did the work correct to check the answer. Would you mind showing me how you did it?

 

[Denis]

Flora, simply replace the "x" with -2.1 in original equation: -3(4x + 3) - 2 = 7 - 2x +3

Left side: -3(4(-2.1) + 3) - 2 = -3(-8.4 + 3) - 2 = -3(-5.4) - 2 = 16.2 - 2 = 14.2

Right side: 7 - 2(-2.1) + 3 = 7 + 4.2 + 3 = 14.2

Remember that multiplying 2 negatives gives a positive; like, -2 times -5 = 10
Kapish?

 

[flora33]

Flora, simply replace the "x" with -2.1 in original equation: -3(4x + 3) - 2 = 7 - 2x +3

Left side: -3(4(-2.1) + 3) - 2 = -3(-8.4 + 3) - 2 = -3(-5.4) - 2 = 16.2 - 2 = 14.2

Right side: 7 - 2(-2.1) + 3 = 7 + 4.2 + 3 = 14.2

Remember that multiplying 2 negatives gives a positive; like, -2 times -5 = 10
Kapish?

Denis, I gotcha. I'm looking at where I made my mistakes. They were simple errors, I put "-5.4" in the place of "-8.4". I think I was just going too fast there, and then with the right side of the equation, I did not remember that multiplying 2 negatives is a positive, and I subtracted 7-4.2 instead of added. Sweeeet, thanks for your help! I know I just need to slow down and check my work sometimes, because I always seem to makes those small mistakes that obviously throw off the whole problem!!

Thanks again!
Flora

 

[Denis]

Denis, I gotcha. I'm looking at where I made my mistakes. They were simple errors, I put "-5.4" in the place of "-8.4". I think I was just going too fast there, and then with the right side of the equation, I did not remember that multiplying 2 negatives is a positive, and I subtracted 7-4.2 instead of added. Sweeeet, thanks for your help! I know I just need to slow down and check my work sometimes, because I always seem to makes those small mistakes that obviously throw off the whole problem!!

You'll have to stop being a "fast woman"

 

[flora33]

Denis, I gotcha. I'm looking at where I made my mistakes. They were simple errors, I put "-5.4" in the place of "-8.4". I think I was just going too fast there, and then with the right side of the equation, I did not remember that multiplying 2 negatives is a positive, and I subtracted 7-4.2 instead of added. Sweeeet, thanks for your help! I know I just need to slow down and check my work sometimes, because I always seem to makes those small mistakes that obviously throw off the whole problem!!

You'll have to stop being a "fast woman"

Seriously! I have that problem! Driving, eating, math... I'm noticing a trend!