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

a = ± 4

Step-by-step explanation:

Expressing the proportion in fractional form

= ( 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 = ± = ± 4

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

where's the diagram?

step-by-step explanation: