tentukan nilai cos P pada segitiga PQR brkt. a. PQ = 15 cm , QR = 10cm , dan

Bab Trigonometri
Matematika SMA Kelas X


A. r = 15 cm , p = 10 cm ,
r / sin R = p / sin P
15 / sin 30 = 10 / sin P
15 / 1/2 = 10 / sin P
15 sin P = 5
sin P = 5/15
sin P = 1/3

Cos^2 p + sin^2 p = 1
Cos^2 p + 1/9 = 1
Cos^2 p = 1 - 1/9
Cos^2 p = 8/9
Cos p = V8 / 3
Cos p = 2 V2 / 3
Cos p = 2/3 V2

B. r = 3cm , p = 5cm , q = 7 cm

p^2 = q^2 + r^2 - 2qr cos P
5^2 = 7^2 + 3^2 - 2.7.3 cos P
25 = 49 + 9 - 42 cos P
25 = 58 - 42 cos P
25 - 58 = - 42 cos P
-33 = -42 cos P
cos P = -33/-42
cos P = 11/14

Semoga membantu;)