a-maths!!!

! a - b !^2
= (a - b)(a - b)
= aa - ab - ba + bb
= aa - 2ab + bb
= !a!^2 - 2!a!!b!cos@ + !b!^2
bi)
! a - b !^2
= 3 - 2 sqrt(3) (2)cos30 + 4
= 7 - 6
= 1
! a - b ! = 1
ii)
! a - b !^2
= 3 - 2 sqrt(3) (2)cos150 + 4
= 7 + 6
= 13
! a - b ! = sqrt(13), 根 13
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