Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Soal-soal<br />
Soal-soal berikut mengacu pada Gambar 2.29.<br />
1. = 60 o ; = 50 o dan b = 10 4. = 35 o ; = 125 o dan c = 7<br />
2. = 70 o ; = 45 o dan c = 20 5. = 25 o ; = 40 o dan a = 5<br />
3. = 30 o ; = 115 o dan c = 8<br />
I. Hukum Cosinus<br />
Untuk membuktikan hukum cosinushatikan Gambar 2.30 berikut.<br />
C<br />
b<br />
<br />
E<br />
a<br />
k<br />
h<br />
<br />
<br />
A D B<br />
c<br />
Gambar 3.30<br />
Perhatikan segitiga ADC h = b sin <br />
Perhatikan segitiga BDC (CD) 2 = (BC) 2 – (BD) 2 = (BC) 2 – (AB - AD) 2<br />
h 2 = a 2 – (c - b cos ) 2<br />
b 2 sin 2 = a 2 – c 2 + 2bc cos - b 2 cos 2 <br />
b 2 sin 2 + b 2 cos 2 = a 2 – c 2 + 2bc cos <br />
b 2 (sin 2 + cos 2 ) = a 2 – c 2 + 2bc cos <br />
b 2 = a 2 – c 2 + 2bc cos <br />
Sehingga,<br />
a b c bc cos a au cos<br />
b c a<br />
bc<br />
( . )<br />
Perhatikan segitiga BDC h = a sin <br />
Perhatikan segitiga ADC (CD) 2 = (AC) 2 – (AD) 2 = (AC) 2 – (AB - BD) 2<br />
h 2 = b 2 – (c - a cos ) 2<br />
a 2 sin 2 = b 2 – c 2 + 2ac cos - a 2 cos 2 <br />
a 2 sin 2 + a 2 cos 2 = b 2 – c 2 + 2ac cos <br />
a 2 (sin 2 + cos 2 ) = b 2 – c 2 + 2ac cos <br />
a 2 = b 2 – c 2 + 2ac cos <br />
Sehingga,<br />
b a c ac cos a au cos<br />
a c b<br />
ac<br />
( . )<br />
65