Answer:
a = ± 4
Step-by-step explanation:
Expressing the proportion in fractional form
[tex]\frac{3}{a-1}[/tex] = [tex]\frac{a+1}{5}[/tex] ( cross- multiply )
(a -1 )(a + 1) = 15 ← expand factors on left side
a² - 1 = 15 ( add 1 to both sides )
a² = 16 ( take the square root of both sides )
a = ± [tex]\sqrt{16}[/tex] = ± 4
