diketahui segitiga ABC dengan panjang sisi b=20, < C=105° dan < B=45°. Hitunglah panjang sisi a dan c . . .

<A + <B + <C = 180
<A + 45 + 105 = 180
<A = 30

sinA = sin30 = 1/2
sinB = sin45 = 1/2√2
sinC = sin105
sin105 = sin(180-75) = sin75 = sin(30+45) = sin30.cos45 + cos30.sin45 
           = 1/2.1/2 √2 + 1/2 √3 .1/2 √2
 sinC   = 1/4 √2 + 1/4 √6

aturan sin
a/sinA = b/sinB = c/sinC

a/sinA = b/sinB
a/(1/2) = 20/(1/2 √2)
a = 20.(1/2)/(1/2 √2)
a = 20/√2
a = 20/2 √2
a = 10√2

c/sinC = b/sinB
c/(1/4 √2 + 1/4 √6) = 20/(1/2√2)
c = 20. 1/4(√2+√6) / (1/2√2)
c = 10(√2+√6)/√2
c = 5√2(√2+√6)
c = 10+5√12
c = 10+10√3

jadi nilai a = 10√2 dan c = 10+10√3