题目

在三角形ABC中,若三内角A,B,C成等差数列,三边a,b,c成等比数列,且a=1,则边c=

分类:数学


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已知a根号下1-b2+b根号下1-a2=1,求证:a2+b2=1 用数形结合证明
a根号1-b² +b根号1-a²=1
两边平方 a²(1-b²)+b²(1-a²)+2ab根号(1-a²-b²+a²b²)=1
整理 1-a²-b²+a²b²-2ab根号(1-a²-b²+a²b²)+a²b²=0
(根号(1-a²-b²+a²b²)-ab)²=0
根号(1-a²-b²+a²b²)=ab
1-a²-b²+a²b²=a²b²
a²+b²=1
log 2 X =3/2 怎么算出x的值来?
X = 2的3/2次方 = 2√2
英语音标补充相同读音的单词.
每题补充3~6个就行,写完(1)~(5)题再写下A组与B组有什么规律.回答就写如(2)A...B...就行
(1)这题是音标a
A name plane jane baby cake
B bag dad hat map black back
(2)e
A he these me chinese
B bed let pen desk yes egg
(3)i
A bike drive time nice kite
B fish big drink sit milk swim
(4)o
A those close go home no
B clock not box shop sock
(5)u
A student excuse duty
B bus cup jump much lunch
1) A :same wake date make wave rage
B:cat bad thank rap sad
2) A:she we be
B:red shell belt net
3) A:ice side prime slide
B:ink pig tin dim this
4) A :joke post glove smoke
B; pot got dog doctor clock
5) A:use cure built useful
B:nut thus such must dust

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三角函数题,求过程!

原式=1/[(2sin20°)/(1+cos20°)] - sin10°[(cos5°/sin5°)-(sin5°/cos5°)]
=1/(2tan10°) - sin10°[(cos²5° - sin²5°)/(sin5°·cos5°)]
=(cos10°)/(2sin10°) - sin10°[cos10°/(1/2)sin10°]
=(cos10°)/(2sin10°) - (4sin10°cos10°)/(2sin10°)
=(cos10° - 2sin20°)/(2sin10°)
=[cos(90°-80°) - 2sin20°]/(2sin10°)
=(sin80° - sin20° - sin20°)/(2sin10°)
=[2·cos(80°+20°)/2·sin(80°-20°)/2 - sin20°)/(2sin10°)
=(2cos50°sin30° - sin20°)/(2sin10°)
=(cos50° - sin20°)/(2sin10°)
=[cos(90°-40°) - sin20°]/(2sin10°)
=(sin40° - sin20°]/(2sin10°)
=[2·cos(40°+20°)/2·sin(40°-20°)/2]/(2sin10°)
=(2cos30°sin10°)/(2sin10°)
=√3/2
计算 (三倍根号6-根号15)的平方
(三倍根号6-根号15)的平方
=54-6√6x√15+15
=69-6√90
=69-18√10
如果本题有什么不明白可以追问,如果满意请点击“选为满意答案”
已知f(x)=2sin(x+θ/2)cos(x+θ/2)+2√3cos²(x+θ/2)-√3,且0≤θ≤π,求使函数f(x)为偶函数的值
f(x)=sin(2x+θ)+2√3[1+cos(2x+θ)]/2-√3
=sin(2x+θ)+√3cos(2x+θ)
=2sin(2x+θ+π/3)是偶函数
f(-x)=f(x)
2sin(-2x+θ+π/3)=2sin(2x+θ+π/3)
所以-2x+θ+π/3=2kπ+2x+θ+π/3或-2x+θ+π/3=2kπ+π-(2x+θ+π/3)
-2x+θ+π/3=2kπ+2x+θ+π/3
4x=-2kπ
不是恒等式
-2x+θ+π/3=2kπ+π-(2x+θ+π/3)
2θ=2kπ+π/3
θ=kπ+π/6
所以θ=π/6

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