sin²20°+sin²25°+√2sin20°sin25°
来源:学生作业帮 编辑:神马作文网作业帮 分类:数学作业 时间:2024/09/24 04:28:28
sin²20°+sin²25°+√2sin20°sin25°
sin²20 + sin²25 + √2sin20sin25
= (1 - cos40)/2 + (1 - cos50)/2 + (√2)(1/2)[cos(20 - 25) - cos(20 + 25)]
= 1 - (1/2)(cos40 + cos50) + (√2/2)(- cos5 - cos45)
= 1 - (1/2)(2)cos[(40 + 50)/2]cos[(40 - 50)/2] - (√2/2)cos5 - (√2/2)(√2/2)
= 1 - cos45cos5 + (√2/2)cos5 - 1/2
= 1/2 - (√2/2)cos5 + (√2/2)cos5
= 1/2
公式:
sin²θ = (1 - cos2θ)/2
sinxsiny = (1/2)[cos(x - y) - cos(x + y)]
cosx + cosy = 2cos[(x + y)/2]cos[(x - y)/2]
= (1 - cos40)/2 + (1 - cos50)/2 + (√2)(1/2)[cos(20 - 25) - cos(20 + 25)]
= 1 - (1/2)(cos40 + cos50) + (√2/2)(- cos5 - cos45)
= 1 - (1/2)(2)cos[(40 + 50)/2]cos[(40 - 50)/2] - (√2/2)cos5 - (√2/2)(√2/2)
= 1 - cos45cos5 + (√2/2)cos5 - 1/2
= 1/2 - (√2/2)cos5 + (√2/2)cos5
= 1/2
公式:
sin²θ = (1 - cos2θ)/2
sinxsiny = (1/2)[cos(x - y) - cos(x + y)]
cosx + cosy = 2cos[(x + y)/2]cos[(x - y)/2]
√(sin²70°)-√(1-2sin20°cos20°)+|sin20°-1|
sin²20°+sin²80°-sin20°sin80°=?
(√1+2sin20°cos20°)/(sin20°+√1-sin^2 20°)
根号(sin²70°)-根号(1-2sin20°×cos20°)+绝对值里(sin20°-1)
sin70°sin65°-sin20°sin25°=( )
化简sin20°分之sin^35°-1/2
三角函数之求值问题sin²20°+cos²50°+sin20°cos50°=sin20°cos50
根号下sin方70°-根号下1-2sin20°cos20°+|sin20°-1|=?
化简(根号下1-2sin20°cos20°)/[(sin20°)-(根号下1-sin平方20°)
sin平方20°+cos平方80°+根号3sin20°cos80°
用和(差)角公式求下列各式的值:(1)sin70°cos25°-sin20°sin25°;(2)cos^2 15°-si
计算:sin²1°+sin²2°+sin²3°...+sin²45°+sin