(cos^2)15°-(sin^2)15等于多少

来源：学生作业帮助网编辑：作业帮时间：2024/11/05 22:32:10

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(cos^2)15°-(sin^2)15等于多少
(cos^2)15°-(sin^2)15等于多少

(cos^2)15°-(sin^2)15等于多少
这是因为:
方法一:
(cos^2)15°-(sin^2)15
=(cos15+sin15)(cos15-sin15)
=[sin(90-15)+sin15][sin(90-15)-sin15]
=(sin75+sin15)(sin75-sin15)
=2*sin(75+15)/2*cos(75-15)/2*2*cos(75+15)*sin(75-15)/2
=4*sin45*cos30*cos45*sin30
=√3/2.
方法二:
cos15°=cos(45-30)=cos45*cos30+sin45*sin30
=√2/2*√3/2+√2/2*1/2
=(√6+√2)/4.
cos^2(15)=[(√6+√2)/4]^2=(2+√3)/4,
sin15=sin(45-30)=sin45*cos30-cos45*sin30
=√2/2*√3/2-√2/2*1/2
=(√6-√2)/4.
sin^2(15)=[(√6-√2)/4]^2=(2-√3)/4.
(cos^2)15°-(sin^2)15=(2+√3)/4-(2-√3)/4
=√3/2.

cos15°=cos(45-30)=cos45*cos30+sin45*sin30 =√2/2*√3/2+√2/2*1/2 =(√6+√2)/4. cos^2(15)=[(√6+√2)/4]^2=(2+√3)/4, sin15=sin(45-30)=sin45*cos30-cos45*sin30 =√2/2*√3/2-√2/2*1/2 =(√6-√2)/4. sin^2(15)=[(√6-√2)/4]^2=(2-√3)/4. (cos^2)15°-(sin^2)15=(2+√3)/4-(2-√3)/4 =√3/2.

(cos^2)15°+(sin^2)15°等于多少 cos^2 15°-sin^2 15°的值 cos^2 15°-sin^2 15°= 求(sin^2)15°(cos^2)15° cos^2 15°—sin^2 15°＝? (cos^2)15°-(sin^2)15等于多少化简:sin^2(75°)*cos^2(15°)-cos^2(75°)*sin^2(15°) 化简:sin^2(75°)*cos^2(15°)-cos^2(75°)*sin^2(15°) 化简1：cos(15°-a)sin15°-sin(165°+a)cos(-15°)2：根号下cos(60°-a)-sin(60°-a) 2sin@+cos@等于? 证明恒等式：（1+sinα)/cosα=(1+tan(α/2))/(1-tan(α/2))还有一道化简：（cos(θ+15°)）^2+（sin(θ-15°)）^2+cos(θ+180°)sin(θ+180°) cos^15°-sin^15°= sin²15° 把sin变成带cos的三角比化简~cos^2(A+15°）+sin^2(A-15°)+sin(A+180°)cos(A-180°)3Q sin^2 30°+cos()=1 化简~cos^2(a+15)+sin^2(a-15)+sin(a+180)cos(a-180)15为15度求证:sin^2/(sin-cos) - (sin+cos)/(tan^2 -1) =sin+cos 若f(cos x)=cos 2x,则f(sin 15度）的值?