※ 引述《lipton (青年阿~要立死志)》之銘言：
: 1.8=0.6 cosA + 0.8√3 cosB
: 0 =0.6 sinA - 0.8√3 sinB
: 如何求解A和B呢?
9 = 3 cos(A) + 4√3 cos(B)...(1)
0 = 3 sin(A) - 4√3 sin(B)...(2)
做三角形ABC, AB=9, AC=3, BC=4√3
由正弦定理, sin(A)/4√3 = sin(B)/3 => 3 sin(A) - 4√3(B) = 0
由投影 => 9 = AB = AC cos(A) + BC cos(B) = 3 cos(A) + 4√3 cos(B)
所以∠A, ∠B是一組解. 餘弦得 cos(A)=7/9, cos(B)=5/(3√3)
(2)知道A,B同在I,II或III,IV，而把角度轉過去帶入都符合(1)
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 59.115.150.167