已知tanα=-1/2,求下列各式的值;sinα+2cosα

1个回答

  • 1.(1)原式=(4tan-2)/(5+3tan)【分子分母同除以tan】

    =10/14

    =5/7

    (2)原式=(sincos)/(sin^2+cos^2)

    =tan/tan^2+1

    =3/9+1

    =3/10

    (3)原式=sin^2+cos^2+2sincos

    =1+2*3/10

    =8/5

    (4)貌似题目有打错了.

    2.sin(π+α)=-sinα=-1/2

    ∴sinα=1/2

    ∴cosα=±根号3/2

    (1)原式=cos(-a)

    =cosa

    =±根号3/2

    (2)原式=-tana=-sina/cosa

    =(-1/2)/(±根号3/2)

    =±根号3/3

    3.(1)

    cos25π/6+cos25π/3+tan(-25π/4)

    =cosπ/6+cosπ/3-tanπ/4

    =根号3/2+1/2-1

    =(根号3-1)/2

    (2)

    sin2+cos3+tan4【无特殊角,只能计算器算】

    sin2≈0.9093

    cos3≈-0.9900

    tan4≈1.1578

    加起来既得:0.0771

    【打了很久,