Tolong bantu, pake caranya ya. Itu pilihan ganda semua

Tolong bantu, pake caranya ya. Itu pilihan ganda semua

No.7
. U3 = a + 2b = 71
U20 = a + 19b = 20
—————————- –
– 17b = 51
b = 51/-17
b = – 3
a + 2b = 71
a + 2(-3) = 71
a – 6 = 71
a = 71 + 6
a = 77

Un = a + (n – 1).b
U60 = 77 + (60 – 1). – 3
U60 = 77 + 59 (-3)
U60 = 77 – 177
U60 = – 100
jawaban :A

no.6
$frac{2 sqrt{3} }{ sqrt{8} - sqrt{6} } = frac{2 sqrt{3}( sqrt{8} + sqrt{6} )}{( sqrt{8} - sqrt{6} )( sqrt{8} + sqrt{6} )} \ = frac{2 sqrt{3} ( sqrt{8} + sqrt{6}) }{8 - 6} \ = frac{2 sqrt{3} ( sqrt{8} + sqrt{6} ) }{2} \ = sqrt{3} ( sqrt{8} + sqrt{6} ) \ = sqrt{24} + sqrt{18} \ = 2 sqrt{6} + 3 sqrt{2}$
no.5
x² + 3x – 5 = 0 ==> a = 1 , b = 3 , c = – 5

A + B = x1 – 1 + x2 – 1
A + B = x1 + x2 – 2
A + B = – b/a – 2
A + B = – 3/1 – 2
A + B = – 5

A.B = (x1 – 1)(x2 – 1)
A.B = x1.x2 – (x1 + x2) + 1
A.B = c/a – (-b/a) + 1
A.B = – (-5/1) – (-3/1) + 1
A.B = 5 + 3 + 1
A.B = 9
bentuk umum persamaan baru
x² – (A + B)x + A.B = 0
x² – (-5)x + 9 = 0
x² + 5x + 9 = 0