Nomor 3,4,9 tolong yak pake cara

3) tan a = a/x
sisi depan a
sisi samping x
sisi miring √(a²+x²)
x/√(a²+x²) = samping/miring = cos a
pilihan B
4) (1+sin a)(1-sin a) / (1+cos a)(1-cos a)
= (1 - sin²a)/(1-cos²a)
= cos²a/sin²a
= cotan²a
= 7/8
9) (sin a + cos a)² + (sin a - cos a)²
= sin²a + 2.sin a.cos a + cos²a + sin²a - 2.sin a.cos a + cos²a
= 2sin²a + 2cos²a
= 2(sin²a + cos²a)
= 2(1)
= 2