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...
catz Posted March 14, 2013 Share Posted March 14, 2013 Ok - the answer book is right. It's because the first -2 is not in parens. You could also write it as ... (-1)(2^2) - (-2)^3 Quote Link to comment Share on other sites More sharing options...
silver Posted March 14, 2013 Share Posted March 14, 2013 The answer key is correct. -22 - (-2)3 =-(22 )- (-2)3 =-4 - (-8) =-4+8 =4 The first part is negative (two squared). So it is -(2*2), not (-2*-2) Quote Link to comment Share on other sites More sharing options...
nmoira 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? -(2^2) - [(-2)^3] = -(4) - [-8] = 4 Think of it as: 0 - 22 - (-2)3 Quote Link to comment Share on other sites More sharing options...
amsunshine Posted March 14, 2013 Share Posted March 14, 2013 Answer book is right. It's because the negative square of 2 is -4. If -2 was in parens, the square of a negative 2 is positive. Clear as mud? Quote Link to comment Share on other sites More sharing options...
Audrey Posted March 14, 2013 Author Share Posted March 14, 2013 Thank you for your responses and explanations. That made it clearer. Somewhere along the way, we both forgot the issue of parentheses. Ds is now very sad that he missed that. But... at least we've learned something! So, it's all good. Quote Link to comment Share on other sites More sharing options...
Sahamamama Posted March 14, 2013 Share Posted March 14, 2013 Audrey, I did the problem without scrolling down to the book answer, and I got what your son got. Now I have to try to figure out why my (our) answer is wrong. I agree, this is befuddling. Quote Link to comment Share on other sites More sharing options...
Sahamamama Posted March 14, 2013 Share Posted March 14, 2013 The answer key is correct. -22 - (-2)3 =-(22 )- (-2)3 =-4 - (-8) =-4+8 =4 The first part is negative (two squared). So it is -(2*2), not (-2*-2) -2(squared) is not equal to (-2)squared? No wonder Algebra was a blur for me. Is there hope to ever understand it? Oldest is now in 2nd grade... :sad: Quote Link to comment Share on other sites More sharing options...
amsunshine Posted March 14, 2013 Share Posted March 14, 2013 Oh, and also another reason -- with the order of operations, exponents are done first. Quote Link to comment Share on other sites More sharing options...
nmoira Posted March 14, 2013 Share Posted March 14, 2013 -2(squared) is not equal to (-2)squared? No wonder Algebra was a blur for me. Is there hope to ever understand it? Oldest is now in 2nd grade... :sad: The exponent acts first unless parentheses are present. -22 = -(22) = - (2 x 2) = -4 OR -22 = (-1) x (22) = (-1) x (2 x 2) = (-1) x (4) = -4 (-2)2 = (-2) x (-2) = 4 Quote Link to comment Share on other sites More sharing options...
ByGrace3 Posted March 14, 2013 Share Posted March 14, 2013 -2(squared) is not equal to (-2)squared? No wonder Algebra was a blur for me. Is there hope to ever understand it? Oldest is now in 2nd grade... :sad: Yup. I missed it too. I think I missed the day on order of operations. :lol: I guess it's a good thing our oldest's are in 2nd. We have time to self educate math! ;) Quote Link to comment Share on other sites More sharing options...
Sahamamama Posted March 15, 2013 Share Posted March 15, 2013 The exponent acts first unless parentheses are present. -22 = -(22) = - (2 x 2) = -4 OR -22 = (-1) x (22) = (-1) x (2 x 2) = (-1) x (4) = -4 (-2)2 = (-2) x (-2) = 4 Ah, I remember now: The Dreaded PEMDAS and the Exponents of Death. Thanks, nmoira! ;) Quote Link to comment Share on other sites More sharing options...
Sahamamama Posted March 15, 2013 Share Posted March 15, 2013 Yup. I missed it too. I think I missed the day on order of operations. :lol: I guess it's a good thing our oldest's are in 2nd. We have time to self educate math! ;) I must have been out that day, too. ;) Quote Link to comment Share on other sites More sharing options...
letsplaymath Posted March 17, 2013 Share Posted March 17, 2013 I remind my kids that the exponent only applies to whatever it "touches": If it touches parentheses, then it squares (or cubes or whatever) everything within the parentheses. But if it's touching a number or a variable, it only applies to that number/variable. Quote Link to comment Share on other sites More sharing options...
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