Question

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Answer 1

Ответ:

Объяснение:

3. (cos a)^2 - 1 = - (sin a)^2

4. 1 - (sin a)^2 = (cos a)^2

5. 1 + (tg a)^2 = (1/cos a)^2

6. (sin a)^2 - 1 = - (cos a)^2

7. tg a = 1/ctg a

8. cos a = $sqrt{(1/(1+(tg a)^2))}$

9. = 1/2 - 1/2 - (-1) = 1

10. = 0 - 1 = -1