Check my answers please

Question: (-10x^3+3x^2-2x+7)(7x^3+9x^2-10x-6)
Answer: -3^3+12x^2-12x-1

Question: 5y(y^2-5y)
Answer: 5y^3-25y^2

Question: 5ab^4(4a^4b^4+6ab)
Answer: 20a^5b^8+30a^4b^5

If you're looking to check your answers then www.wolframalpha.com is your best friend. It's an information search engine, type in your expression and it will simplify it for you (as well as thousands of other things it can do).

Question 1 is wrong, the answer will be a polynomial with highest order 6, because at some point you're multiplying x^3 and x^3. If you don't have x^6 somewhere in your answer you've gone wrong.

Question 2 is right, well done!

Question 3 is almost right, only one of your numbers is wrong (check the index of your a term in the 30a^4b^5)

Good on you for having a go yourself and asking for checked answers instead of asking people to do it for you.

EDIT: ah yes I should've noticed how close your first answer is to a different question. If the question is (-10x^3+3x^2-2x+7)+(7x^3+9x^2-10x-6) then you have the right answer. So Q3 is the only one to look at.

1 is totally wrong. Hint: The last term would be 7 * -6 = -42

and I think your eyes shifted when doing #3 because a term is wrong.

EDIT: on Sasquatches' edit: you are missing the x in the first term in #1 - - otherwise, yes, now that I know you are adding.

answer 1
------------ ans 1 is incorrect.

the last term is 1 in your answer which can't be so as only 7&6 are 2 constants multiplying herein.

ans 2- correct

ans 3 - last part 5 ab^4*6 ab = 30 a^2b^5

The second two are correct, but shouldn't there be a positive sign between the brackets in the first one? If so then it is correct too.