Tolong ka bantu kerjakan​

Jawab:

Penjelasan dengan langkah-langkah:

3. Luas = (1/2) × PR × QR × sin R

= (1/2) × 15 × 8 × sin 120

= 60 × ((akar 3) /2)

= 30 akar 3

4. Sin 75 = sin (30 + 45)

= sin 30 cos 45 + cos 30 sin 45

= (1/2)((akar 2)/2) + ((akar 3)/2)((akar 2)/2)

= (akar 2)/4 + (akar 6)/4

= (akar 2 + akar 6) / 4

Cos 165 = cos (120 + 45)

= cos 120 cos 45 – sin 120 sin 45

= (-1/2)((akar 2)/2) – ((akar 3)/2)((akar 2)/2)

= -(akar 2)/4 – (akar 6)/4

= -(akar 2 + akar 6)/4

5. Sin A = 3/5 ; sin B = 7/25

Cos A = akar kuadrat (1 – (3/5)^2)

= akar kuadrat (1 – 9/25)

= akar kuadrat 16/25

= 4/5

Cos B = akar kuadrat (1 – (7/25)^2)

= akar kuadrat (1 – 49/625)

= akar kuadrat (576/625)

= 24/25

Cos (A + B) = Cos A cos B – sin A sin B

= (4/5)(24/25) – (3/5)(7/25)

= 96/125 – 21/125

= 75/125

= 3/5