segitiga DEF mempunyai keliling 70cm. jika panjang sisi EF =25 dan DF =17cm berapa luas segitiga tersebut

DE = 70 - 25 + 17 = 28 cm


diketahui :
a=28 cm
b=25 cm
c= 17 cm

s = 1/2 (a+b+c)
s = 1/2 (28+25+17)
s = 1/2 x 70
s = 35 

L = √s(s-a)(s-b)(s-c)
L = √35(35-28)(35-25)(35-17
L = √35 x 7 x 10 x 17
L = √41650
L = 204.08 m

∆DEF , misalnya
sisi EF = d = 25
Sisi DF = e = 17
Sisi DE = f

Keliling = 70
d + e + f = 70
25 + 17 + f = 70
f = 70 - 42 = 28

S = 1/2 (d + e + f) = 1/2 (70) = 35

Luas = √(S (S - d) (S - e) (S - f))
= √(35 (35 - 25) (35 - 17) (35 - 28))
= √(35 (10) (18) (7))
= √(44100)
= 210 cm^2