Thread: Add subtract polynomials, Multiplying with monomials

Originally Posted by fyisvd

Im having trouble with three problems.

1.Simplify (-5b*3x)*4.

I got 626b*7x*4

2. Simplify -2x(x-3) + x(5-x).


3. Multiply: a*2b - 3ab*2 +5b*3

-2ab
_________________

I got -2a*3b*2 + 6a*2b*3 - 10ab*4

1. How did you get that answer for 1? are you sure you typed the problem correctly? becuase * means multiply, you would end up with

-60xb

2. Simplify -2x(x-3) + x(5-x)

First we expand the brackets for -2x(x-3) we multiply everything in the brackets by -2x to get -2x^2 + 6x, for the x(5-x) we multiply everything in the brackets by x to get 5x - x^2, so we end up with something like this

-2x(x-3) + x(5-x) = -2x^2 + 6x + 5x - x^2 = -3x^2 + 11x

3. I assume your question is: Multiply: a*2b - 3ab*2 +5b*3
by -2ab. Okay, can you clarify for me. do you use the * to mean a power? for example when you type a*2, do you mean a squared?

Yes i meant a power when i used *. Im sorry i should have carified that. Do you use something different on this site. Im just used to using*.

Originally Posted by fyisvd

Yes i meant a power when i used *. Im sorry i should have carified that. Do you use something different on this site. Im just used to using*.

Yes, we use ^. so everywhere i see * i should just read ^, okay got it

Originally Posted by fyisvd

Im having trouble with three problems.

1.Simplify (-5b^3*x)^4.

I got 626b^7x^4

2. Simplify -2x(x-3) + x(5-x).


3. Multiply: a^2*b - 3ab^2 +5b^3 by -2ab
_________________

I got -2a^3*b^2 + 6a^2*b^3 - 10ab^4

Note: * means "multiply", ^ means "to the power"

1.Simplify (-5b^3*x)^4

Okay, first let us recall some rules.

(ab)^c = a^c * b^c or similarly (a^x*b^y)^c = a^(x*c) * b^(y*c)

okay, so we have (-5)^4 * (b^3)^4 * x^4 = 625b^12*x^4 .....we multiply the powers in this case, not add, so we get b^12 not b^7 as you had.

When do we add powers? We do that when multiplying simialr bases, that is,
b^a * b^c = b^(a + c)

2. Simplify -2x(x-3) + x(5-x), i believe this question was okay to begin with, no confusion here, check my one of my previous posts for the answer.


3. Multiply: a^2*b - 3ab^2 +5b^3 by -2ab

so we have -2ab(a^2*b - 3ab^2 +5b^3) we multiply each term by -2ab to obtain:

-2 * a*a^2 * b*b -2(-3)*a*a * b*b^2 + (-2)(5)*a*b*b^3
= -2a^3*b^2 + 6a^2*b^3 - 10ab^4

Thank you. It makes sense to me now.