Audrey Posted March 14, 2013 Share Posted March 14, 2013 The question is: -22 - (-2)3 Ds's answer is: -22 - (-2)3 = 4 - (-8) = 4+8 = 12 The answer key says: -22 - (-2)3 = -4 -(-8) = -4 + 8 = 4 Who is right? And if ds is wrong, why? Quote Link to comment Share on other sites More sharing options...
elegantlion Posted March 14, 2013 Share Posted March 14, 2013 I think your son is right. The only reason I can think that the book would be right is if it was written -(2^2). I would read it as -2 not - times 2. Quote Link to comment Share on other sites More sharing options...
ondreeuh Posted March 14, 2013 Share Posted March 14, 2013 I thought that -2^2 meant -(2^2). If you want to square -2, you have to put the -2 in parentheses: (-2)^2. Quote Link to comment Share on other sites More sharing options...
ondreeuh Posted March 14, 2013 Share Posted March 14, 2013 http://www.purplemath.com/modules/negative4.htm says I'm right. Quote Link to comment Share on other sites More sharing options...
EKS Posted March 14, 2013 Share Posted March 14, 2013 I thought that -2^2 meant -(2^2). If you want to square -2, you have to put the -2 in parentheses: (-2)^2. This is correct. Quote Link to comment Share on other sites More sharing options...
Audrey Posted March 14, 2013 Author Share Posted March 14, 2013 Thank you. We now see where we went wrong. Poor ds. He was really convinced he was right. But, now we've learned something! So, it's all good. :) Quote Link to comment Share on other sites More sharing options...
Dana Posted March 15, 2013 Share Posted March 15, 2013 The illustration I use for why -2^2 is -4 and not +4 is this... If you had 7-2^2 as your problem, you'd write your next step as 7-4, not 7+4 In this way, if the 7 weren't there, we need -2^2 tobe -4, otherwise we've got a problem when the 7 is there... We need consistency. Also...order of operations...the base is 2, then it's being negated. We must have parentheses if we wanted the base to be -2. Quote Link to comment Share on other sites More sharing options...
elegantlion Posted March 15, 2013 Share Posted March 15, 2013 Thank you. We now see where we went wrong. Poor ds. He was really convinced he was right. But, now we've learned something! So, it's all good. :) I get it now too. Quote Link to comment Share on other sites More sharing options...
Barb_ Posted March 15, 2013 Share Posted March 15, 2013 Don't feel badly. I'm on my fourth time around teaching Algebra 1 and that litfle piece of PEDMAS trips me up Every. Single. Time. And math is generally known to be my best topic. Without looking at your son's work, I got the same answer he did, but when I looked at the solution I was like, "aaaaargh! Not again!" Quote Link to comment Share on other sites More sharing options...
ILiveInFlipFlops Posted March 15, 2013 Share Posted March 15, 2013 Whoa. I got the right answer, but for the wrong reason, so this discussion just made me want to cry! I am so not looking forward to teaching algebra. (At least I get it now though!) Quote Link to comment Share on other sites More sharing options...
mamajudy Posted March 16, 2013 Share Posted March 16, 2013 Saxon explains it by illustrating a finger covering the first negative sign. You square the 2, then remove your finger. In the case of the second 2, the negative sign is "protected by parentheses." Therefore, you cube the negative 2. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.