Question

Найдите cos a, если sin a =-0,8, 180

Answer 1

Sin^2a+cos^2a=1
cos^2a=1-sin^2a
cos^2a=1-(-0.8)^2
cos^2a=1-0.64
cos^2a=0.36
cosa=√0.36
cosa=0.6

если 0.6 ∈ (90;180) то знак будет минус т.е -0.6

если 0.6 ∈ (180; 270) то знак будет минус т.е -0.6

ответ: -0.6

Answer 2

sin(a) = -0.8 We know that sin^2(a) + cos^2(a) = 1 So, cos^2(a) = 1 - sin^2(a) cos^2(a) = 1 - (-0.8)^2 cos^2(a) = 1 - 0.64 cos^2(a) = 0.36 cos(a) = ±√0.36 cos(a) = ±0.6

Since the angle a is in the second quadrant (180 degrees), and cosine is negative in the second quadrant, the value of cos(a) is -0.6.