Question

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

Answer 1

a = ± 4

Explanation:

Expressing the proportion in fractional form

`(3)/(a-1)` =
`(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 = ±
`√(16)` = ± 4