AD/EF = (AE + BE)/BE kesebangunan

EF/9 = 7/10

EF = 63/10 = 6,3 cm

GF = (6,3 -4)/2 kesebangunan

GF = 2,3/2

GF = 1,15 cm

GC = √(CF² -GF²) phytagoras

GC = √(7² -(1,15)²)

GC = √(19.071/400)

GC = 3/20 √2.119

sin <GCF = GF/CF = 1,15/7 = 23/140

cos <GCF = GC/CF = 3/140 √2.119

<GCF + 90° = <BCF

cos (<GCF + 90°) = cos <GCF cos 90° -sin <GCF sin 90° trigonometri

cos (<BCF) = (3/140 √2.119) (0) -(23/140)(1)

cos (<BCF) = -23/140

BF² = BC² + CF² -2.BC.CF cos <BCF aturan cosinus

BF² = 4² + 7² -2(4)(7) (-23/140)

BF² = 16 + 49 -56 (-23/140)

BF² = 65 + 9,2

BF² = 74,2

BF² = √(1.855/25)

BF = ⅕√1.855 atau 8,614 cm