1# sec² θ – 1 / sec² θ = sin² θ
2# (sec B – cosec B) (sin B + cos B) = tan B – cotan B
Buktikan identitas trigonometri :
ID Trigonometri
no. 1
sec a = 1/cos a
sin² a + cos² a = 1
•
(sec² θ – 1 )/ sec² θ
= (sec² θ / sec² θ) – (1/sec θ)
= 1 – cos² θ
= sin² θ
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no. 2
csc a = 1/sin a
•
(sec B – cosec B) (sin B + cos B)
= sec B sin B + sec B cos B – cosec B sin B – cosec B cos B
= (sin B/cos B) + (cos B/cos B) – (sin B/sin B) – (cos B/sin B)
= tan B + 1 – 1 – cotan B
= tan B – cotan B
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