Question

If 3,a-1,a+1 and 5 are pproportional,then a =?

Answer 1

Answer:

a = ± 4

Step-by-step explanation:

Expressing the proportion in fractional form

$\frac{3}{a-1}$ = $\frac{a+1}{5}$ ( 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 = ± $\sqrt{16}$ = ± 4