a泧(一兀⼀3,兀⼀2,且cos(a+兀⼀3)=1⼀3,求sin(2a+5兀⼀3)的值

2025-05-11 15:12:10
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回答1:

解:∵a∈(-π/3,π/2),则a+π/3∈(0,5π/6)
∴sin(a+π/3)>0
∵cos(a+π/3)=1/3
∴sin(a+π/3)=√(1-(cos(a+π/3))^2)=2√2/3
故sin(2a+5π/3)=sin(π+2(a+π/3))
=-sin(2(a+π/3)) (应用诱导公式)
=-2sin(a+π/3)cos(a+π/3)
=-2(2√2/3)(1/3)
=-4√2/9。