Perhatikan gambar belah ketupat berikut jika AD = (2x + 5), BC = (x + 7), sudut BCD =60° maka tentukan

AD = 2x + 5

BC = x + 7

<BCD = 60°

Besar sudut bangun segitiga adalah 180°

❀ Nilai x ❀

AD = BC

2x + 5 = x + 7

2x – x = 7 – 5

x = 2

❀ Panjang sisi AD ❀

AD = 2x + 5

= 2(2) + 5

= 4 + 5

= 9 cm

❀ Besar sudut BAD ❀

<BAD = <BCD = 60°

❀ Besar sudut ABC ❀

<ABC = 180 – (90 + 60)

= 180 – 150

= 30°

Jawaban:

a. nilai x

2x + 5 = x + 7

2x – x = 7 – 5

x = 2

b. Pj. AD = 2x +5

= 2 × 2 + 5

= 4 + 5

= 9

c. sudut BAD = sudut BCD = 60°

sudut ABC = sudut ADC

sudut ABC = (360° – (60° + 60°)) : 2

= (360° – 120°) : 2

= 240° : 2

= 120°