Jawaban:

Luas persegi panjang = p × l

Keliling persegi panjang = 2(p + l)

Pembahasan

a. Panjang = 14 cm

Keliling = 48 cm

Lebar = .... ? Luas = ... ?

Jawab

Keliling = 48 cm

2(p + l) = 48 cm

(p + l) = \frac{48 \: cm}{2}

14 cm + l = 24 cm

l = 24 cm – 14 cm

l = 10 cm

Lebar = 10 cm

Luas = p × l

Luas = 14 cm × 10 cm

Luas = 140 cm²

b. Panjang 20 cm

Luas = 640 cm²

Lebar = ... ? Keliling = ... ?

Jawab

Luas = 640 cm²

p × l = 640 cm²

20 cm × l = 640 cm²

l = \frac{640 \: cm^{2}}{20 \: cm}

l = 32 cm

Lebar = 32 cm

Keliling = 2(p + l)

Keliling = 2(20 cm + 32 cm)

Keliling = 2(52 cm)

Keliling = 104 cm

c. Lebar = 12 cm

Keliling = 84 cm

Panjang = ... ? Luas = ... ?

Jawab

Keliling = 84 cm

2(p + l) = 84 cm

(p + l) = \frac{84 \: cm}{2}

p + 12 cm = 42 cm

p = 42 cm – 12 cm

p = 30 cm

Panjang = 30 cm

Luas = p × l

Luas = 30 cm × 12 cm

Luas = 360 cm²

d. Lebar = 30 cm

Keliling = 130 cm

Panjang = .... ? Luas = .... ?

Jawab

Keliling = 130 cm

2(p + l) = 130 cm

(p + l) = \frac{130 \: cm}{2}

p + 30 cm = 65 cm

p = 65 cm – 30 cm

p = 35 cm

Panjang = 35 cm

Luas = p × l

Luas = 35 cm × 30 cm

Luas = 1.050 cm²