math ?

[gatorboy]

Hi, help my son combine like terms....

(2a + 3z) x (4a - 2z) =

Is this correct? 8a x (-6z)

Thx

[KQ]

The Math Page - Adding Like Terms

[digitaldeath]

math doesnt do shit

teach your son how to scam

[iamTRuTH]

assuming x= multiply, then FOIL is your friend = First, Outside, Inside, Last

F = (2a) x (4a) = 8a^2
O = (2a) x (-2z) = -4az
I = (3z) x (4a) = 12az
L = (3z) x (-2z) = -6z^2

Combine terms = 8a^2 -4az +12az -6z^2

Answer = 8a^2 + 8az - 6z^2

[gatorboy]

The Math Page - Adding Like Terms

I actually went there first....but I don't see the two variables (one + and the other -) being multiplied.

The subtraction symbol is where he (ok...we) are having a problem.

[XXX-er]

I flunked math 12 and highschool but they gave me a pass cuz the math/science faculty were afraid I would come back and make their life hell the next year, 9 months later I got into IBM strictly on my ability to drink/smoke/party and fix a hopped up 67 mustang

[Timberridge]

Hi, help my son combine like terms....

(2a + 3z) x (4a - 2z) =

Is this correct? 8a x (-6z)

Thx

With these, one way to check your answer is make the a and z = some number like 1. Solve both sides.

Or use the FOIL method

or pm klar

[iamTRuTH]

Or use the FOIL method

You mean like this

assuming x= multiply, then FOIL is your friend = First, Outside, Inside, Last

F = (2a) x (4a) = 8a^2
O = (2a) x (-2z) = -4az
I = (3z) x (4a) = 12az
L = (3z) x (-2z) = -6z^2

Combine terms = 8a^2 -4az +12az -6z^2

Answer = 8a^2 + 8az - 6z^2

[Buster Highmen]

Multiplication distributes over addition:
A*(B+C) == A*B + A*C. and (B+C)*A == B*A + C*A

So (x+y) * (u+v) == (x+y)*u + (x+y)*v == x*u+y*u + x*v + y*v.

At one point, math could make you a multimillionaire. I don't know if that works anymore.

and I make mistakes...

[frorider]

Multiplication distributes over addition:
A*(B+C) == A*B + A*C. and (B+C)*A == B*A + C*A

So (x+y) * (u+v) == (x+y)*u + (x+y)*v == x*u+y*u + x*v + y*v.

At one point, math could make you a multimillionaire. I don't know if that works anymore.

FIFY

[Buster Highmen]

FIFY

The adload got me again.

[2bjenny]

I guess another way of looking at it......

2a + 3z
4a - 2z
_____________
8a^2 + 12az
- 4az - 6z^2
_____________
8a^2 + 8az - 6z^2

[adrenalated]

FOIL.

Also, if you can't explain the method, then you're completely defeating the purpose of your son learning this to begin with.

[Danno]

hire a tutor

or tell him that the world needs ditchdiggers too.

[fatnslow]

I don't think they teach foil any more. They use a tile method that confuses the fuck out of me when my oldest was learning. I showed him foil and ended up confusing the fuck out of him. Download photo math app and it will save you and your kid alot of grief.

[riser4]

I don't think they teach foil any more. They use a tile method that confuses the fuck out of me when my oldest was learning. I showed him foil and ended up confusing the fuck out of him. Download photo math app and it will save you and your kid alot of grief.

What they have done with math instruction in schools should be considered criminal. I blame this guy for what they did to VT schools: https://en.wikipedia.org/wiki/Kenneth_I._Gross

[LongShortLong]

Do our students lern good with tiles?

Sure looks confusing, though I can see some conceptual advantages when it comes to completing the square. When I learned algebra, we did axioms and theorems, and then applied them. FOIL didn't mean much to me, I just applied distributive theorem twice.

Hopefully some education wizard verified that these new approaches produce kids who laugh at (and vote out) the politicians who cut 'millions' from a trillion dollar budget.

To OP's question, think of -2 as +(-2). It's just a negative coefficient. And below I simplified by solving a different, similar problem, so you see the minus sign without the FOIL / cross multiply / whatever they call it these days.
(3z) x (4a - 2z) =
(3z) x (4a + (- 2)*z) = i.e. -2 is the coefficient of z.
3z x 4a + 3z x (-2)z = multiplied out the coefficients and unknown (a and z)
12za + (-6)z^2 = that's a z squared
12az - 6z^2 Changed the above to reflect conventions: pop the minus sign back out from the coefficient, and rearrange the unknowns to alphabetic order. Note that mathematically, all the formulas are equivalent and valid. The first and last formulas are conventional ways to write the formula. First shows a product of 3z and (4a - 2z). Last shows the result.

Hope it's clearer than mud.

[billyk]

When you are doing equations like this, and you are not sure of the answer, it is sometimes a good idea to "sanity check" your answer. In this case, a and z are variables. Try setting them to a few values and see if your answer makes sense. For example, if you set both a=z=1, then (2+3)x(4-2)= 5x2=10. Whereas in your first answer, 8x (-6) = -48, which is clearly wrong.

Sanity checking won't prove that an equation is right all the time, especially if you are using small numbers like 1 to check with, but it is a useful tool to make math tangible and real, rather than just some abstract symbols.