cos+α+π+等于什么

靳征馥3211cos(2π+α)为什么等于cosα -
阚秋戴18390963702 ______ 余弦函数是周期函数,周期是2π,所以它们相等.

靳征馥3211cos( - a - π)为什么=cos(π+a) -
阚秋戴18390963702 ______[答案] 这个利用的是诱导公式 cos(-x)=cosx 令x=a+π, 即得 :cos(-a-π)=cos(π+a)

靳征馥3211用公式证明cos(a+3π)= - cosa -
阚秋戴18390963702 ______[答案] cos(a+3π)=cos(2π+π+a) 根据cos(2π+a)=cos(a) 所以cos(a+3π)=cos(2π+π+a)=cos(π+a) 根据奇变偶不变 符号看象限的原理可知cos(π+a)=-cosa 因为π+a处于第三象限cos为负值所以cosa前面有负号

靳征馥3211cos( - α - π/2)= -
阚秋戴18390963702 ______ cos(-α-π/2)=cos(α+π/2)=-sina

靳征馥3211已知tan(3π/2 + α)=根号下3,那么cos(α+7/2π)= -
阚秋戴18390963702 ______[答案] tan(3/2π+α) =√3; tan(π+π/2+a)=tan(π/2+a)=-cota=√3; cos(α+7/2π)=cos(a+3π/2+2π)=cos(a+3π/2) =cos(a+π/2+π)=-cos(a+π/2)=sina=1/2

靳征馥3211sin(π+α)比上cos(π+α)等于什么 -
阚秋戴18390963702 ______[答案] sin(π+α)比上cos(π+α) =tan(π+α) (利用同角关系式) =tanα (利用诱导公式)

靳征馥3211cos( - π/2+a) 等于什么 -
阚秋戴18390963702 ______[答案] sin a

靳征馥3211设α为锐角,若cos(α+π/3)=4/5,则sin(2α+π/6)=? -
阚秋戴18390963702 ______[答案] sin(2α+π/6) =sin(α+π/3+α-π/6) =sin(α+π/3)cos(α-π/6)+cos(α+π/3)sin(α-π/6) =sin(α+π/3)cos(α+π/3-π/2)+cos(α+π/3)sin(α+π/3-π/2) =3/5*3/5+4/5*(﹣4/5) =﹣7/25

靳征馥3211若cos(a+π/6)=1/4,则sinasin(a+π/3)= - -
阚秋戴18390963702 ______[答案] cos(a+π/6)=cosacosπ/6-sin a sinπ/6=(√3/2)cosa-1/2sina=1/4 [(√3/2)cosa-1/2sina]^2=1/4+1/2cos^2a-(√3/2)sinacosa=1/16 1/2sin^2a=1/2-[-3/16+(√3/2)sinacosa]=11/16-(√3/2)sinacosa sinasin(a+π/3)=sinasinacosπ/3+sinacosasinπ/3=1/2sin^2a+(√...

靳征馥3211cos(α+β)=3/5 ,sin(β - π/4)=5/13,α,β∈0,π/2 则cosα+π/4等于多少
阚秋戴18390963702 ______ 因为cos(α+β)=3/5 ,sin(β-π/4)=5/13,α,β∈0,π/2所以sin(α+β)=4/5,cos(β-π/4)=12/13 所以cos(α+π/4)=cos[a+β-(β-π/4)]=cos(a+β) cos(β-π/4)+sin(a+β)sin(β-π/4)=3/5乘以12/13+4/5乘以5/13=56/65