diketahui cos 1/2 a = 1/4. Nilai cosec a = .... a.7/8 b.1/8akar15 c.-1/7 akar 15 d.-3/4 e.-7/8

cos1/2a=1/4
sin1/a = √15 : 4

Kelas 10 Matematika
Bab Trigonometri

cos (a/2) = 1/4
+- √((1 + cos a)/2) = 1/4
(1 + cos a)/2 = (1/4)²
1 + cos a = 2 . 1/16
cos a = (1/8) - 1
cos a = -7/8 → x/r

y = √(r² - x²)
y = √(8² - (-7)²)
y = √(64 - 49)
y = √15

cosec a = r/y
cosec a = 8/√15
cosec a = (8/15) √15