SOLUTION: If x= -1 and y= 2, What is the value of the expression 2x^3 - 3xy I have tried 2(-1)^3-3(-1)(2) 2(-3) - -3(2) -6 - -6 answer 0

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: If x= -1 and y= 2, What is the value of the expression 2x^3 - 3xy I have tried 2(-1)^3-3(-1)(2) 2(-3) - -3(2) -6 - -6 answer 0       Log On


   

Question 423106: If x= -1 and y= 2, What is the value of the expression 2x^3 - 3xy
I have tried 2(-1)^3-3(-1)(2)
2(-3) - -3(2)
-6 - -6
answer 0

I have an answer sheet and it says the answer is 4. I can not, to save my life figure out how they came up with 4. PLEASE HELP!!!!
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
2x^3 - 3xy

2(-1)^3 - 3(-1)(2)

2(-1) - 3(-1)(2) .... this is where you made the mistake (-1)^3 = -1 NOT -3

2(-1) - 3(-2)

-2 - (-6)

-2 + 6

4


So 2x^3 - 3xy = 4 if x = -1 and y = 2


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