赞 sunwei0414 幼苗
共回答了20个问题采纳率：95% 举报
(1)
a*b
=|a|*|b|*cos60
=2*1*(1/2)
=1
(2)
|a+b|
=根号[(a+b)^2]
=根号[a^2+b^2+2a*b]
=根号[|a|^2+|b|^2+2*1]
=根号[4+1+2]
=根号7
a*b
=|a|*|b|*cos60
=2*1*(1/2)
=1
(2)
|a+b|
=根号[(a+b)^2]
=根号[a^2+b^2+2a*b]
=根号[|a|^2+|b|^2+2*1]
=根号[4+1+2]
=根号7
1年前
2
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