Tolong bantu kerjain soal vektor ini ya teman-teman :(

a . b = |a| . |b| cos θ
a . b = |a| . |b| cos 90
a . b = |a| . |b| . 0
a . b = 0

a(a + b)
= |a|² + a . b
= 3² + 0
= 9 + 0
= 9

jawaban ada di pilihan E