a)hitung luas abc b) hitung AB

AD² = BD·CD
AD² = 4·5
AD = 2√5
a) Luas ΔABC = [tex] \frac{1}{2} [/tex]·9·2√5 = 9√5
b) AB² = BD·BC
    AB² = 4·9
    AB = 6

Rumus pengembanyan phytgoras :
AB² = BD·BC
AC² = CD·BD
AD² = BD·CD

<A = 90
<B=<C = 45

Sin B = 1/2√2
AC/BC = 1/2√2
AC/9 = 1/2√2
AC = 9/2√2

Cos B = 1/2√2
AB/BC = 1/2√2
AB/9 = 1/2√2
AB = 9/2√2

L = AB.AC/2
L = (9/2√2 . 9/2√2) / 2
L = 20,25 cm²

Maaf kalo salah