Question

Tolong .....mohon bantuannya

Answer 1

1)
A(-1,1,4)
B(2, 1, -2)

AC : AB = 4 : -1
4AB = - AC
4(b-a) = - (c-a)
4b - 4a = a - c
c = 5a - 4b
c = 5(-1,1,4) - 4(2,1,-2)
c= (-5, 5, 20)- (8, 4, -8)
c = (-13, 1, 28)

2.
|a| =3
|b| = 4
|a+b| = 5

|a+b|² = |a|² + |b|² + 2 |a||b|
2 a.b = a² +b² - (a+b)²
2 a b = 3² +4² - 5²
ab = 0
jijka a b = 0 maka cos α = 0 = cos 90

sin 2α = sin 2(90)= sin 180 = 0