diketahui segitiga KLm mempunyai penjang sisi KM 10 cm dan KL : 8cm jika nilai cos (L+M):9/40 panjang sisi LM:...... cm

L + M + K = 180°
L + M = 180° - K
Cos (L + M) = cos (180° - K)
9/40 = - cos K
Cos K = -9/40

LM^2 = KM^2 + KL^2 - 2 . KM . KL . Cos K
LM^2 = 10^2 + 8^2 - 2 . 10 . 8 . (-9/40)
LM^2 = 100 + 64 + 36
LM^2 = 200
LM = √200 = 10√2 cm