Multiply (2x+3)(5x-7)

Question

I'm doing a practice sheet and I think I have the correct answer (confirmed by Mathway too)

 

10x^2 + x - 21

 

but the answers on my sheet are

 

[A] 7x^2 - 6x – 21

[B] 10x^2 + 29x – 21

[C] 2x + 15x – 7
[D] 10x2 – 21

and then [E] None of these

 

I want to go with E but then I realized I'm not totally sure. It's really stupid, but I can't find an answer...does the missing x in answer [D] make the answer wrong? Does X have any real value/importance in the answer I got?

again, I realize it might be a stupid question, but I want to know for sure for future reference.

 

Thanks!

Answer 1

(2x+3)(5x-7) = 2x(5x-7) + 3(5x-7) = 2x(5x) + 2x(-7) + 3(5x) + 3(-7)

 

= 10x^2 -14x + 15x - 21 = 10x^2 + (-14+15)x - 21

 

= 10x^2 + x - 21

 

I agree with you that none of the above are correct, so the answer is (E).  (D) is wrong, as per the solution above.  The missing x in (D) is crucial.