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Bab Trigonometri
Matematika SMA Kelas X

[1]
= sin (90° – α) / sin (90° + α)
= [cos α] / [- cos α]
= – 1

[2]
= cos (90° – α) / sin (90° + α)
= [sin α] / [- cos α]
= – tan α

[3]
= sec (90° – α) / cosec (180° + α)
= [1/cos (90° – α)] / [1/sin (180° + α)]
= [1/sin α] / [1/(- sin α)]
= – 1

[4]
P + Q + R = 180°
P = 180° – (Q + R)

[a] cos P = cos [180° – (Q + R)]
cos P = – cos (Q + R)
– cos P = cos (Q + R)

[b] sin P = sin [180° – (Q + R)]
sin P = sin (Q + R)

[c] 
P = 180° – (Q + R)
¹/₂.P = 90° – ¹/₂.(Q + R)
sin (¹/₂.P) = sin [90° – ¹/₂.(Q + R)]
sin (¹/₂.P) = cos [¹/₂.(Q + R)]

selesai
silahkan ditandai sebagai jawaban terbaik sekedar penambah semangat