perhatikan gambar disamping. jika keliling segitiga PQR = 30cm maka luas segitiga PQR adalah... a.30cm² b.28cm² c.27cm² d.25cm²

Keliling = sisi1 + sisi2 + sisi3
30 = 3x+1 + x+1 + 3x
30 = 7x + 2
30 - 2 = 7x
28 = 7x
x = 28/7
x = 4 cm

Luas ∆PQR = ½ . PQ . PR
L = ½ . (x+1) . (3x)
L = ½ . (4+1) . (3.4)
L = ½ . 5 . 12
L = 30 cm² ✔

Jadi, luas ∆PQR 30 cm².

3x + x+1 + 3x+1 = keliling
7x + 2 = 30
7x = 30-2
x = 28/7
x = 4

substitusi x = 4

alas = x+1 = 5
tinggi = 3x = 12

Luas segitiga PQR

= [tex] \frac{1}{2} [/tex] x alas x tinggi
= [tex] \frac{1}{2} [/tex] x 5 x 12
= [tex] \frac{1}{2} [/tex] x 60
= 30 [tex]cm^2[/tex]

Jadi luas segitiga PQR adalah 30 [tex]cm^2[/tex]

Jawaban A