$A=\dfrac{cos7x-cos8x-cos9x+cos10x}{sin7x-sin8x-sin9x+sin10x}$

Question

$A=\dfrac{cos7x-cos8x-cos9x+cos10x}{sin7x-sin8x-sin9x+sin10x}$

in progress 0
Ngọc Khuê 5 years 2021-04-18T22:58:12+00:00 1 Answers 36 views 0

Answers ( )

  1. hongcuc2
    0
    2021-04-18T22:59:38+00:00
    Reply

    Đáp án:

    `A=cot \ {17}/2x` 

    Giải thích các bước giải:

    Ta có:

    `A={cos7x-cos8x-cos9x+cos10x}/{sin7x-sin8x-sin9x+sin10x}`

    `A={(cos7x-cos9x)+(cos10x-cos8x)}/{(sin7x-sin9x)+(sin10x-sin8x)`

    `A={-2sin8xsin(-x)-2sin9xsinx}/{2cos8xsin(-x)+2cos9xsinx}`

    `A={2sin8xsinx-2sin9xsinx}/{-2cos8xsinx+2cos9xsinx}`

    `A={2sinx(sin8x-sin9x)}/{2sinx(cos9x-cos8x)}`

    `A={sin8x-sin9x}/{cos9x-cos8x}`

    `A={2cos\ {17}/2x . sin\ {-x}/2}/{-2sin\ {17}/2x . sin \ x/2}`

    `A={cos\ {17}/2 x}/{sin\ {17}/2 x}`

    `A=cot \ {17}/2x` 

Leave an answer

Browse

Giải phương trình 1 ẩn: x + 2 - 2(x + 1) = -x . Hỏi x = ? ( )