Question

Find the 4th proportional to.3,7 and 9

Answer 1

The 4th proportional of 3, 7 and 9 is 21.

Step-by-step explanation:

Let the 4th proportional of 3, 7 and 9 is x.

3 : 7 : : 9 : x

To find, the 4th proportional of 3, 7 and 9 = ?

∴ 3 : 7 : : 9 : x

Here, a = 3, b = 7, c = 9 and d = x

We know that,

Product of means = Product of extremes

⇒ a × d = b × c

⇒ 3 × x = 7 × 9

⇒ 3x = 63

⇒ x = 21

∴The 4th proportional of 3, 7 and 9 = 21

Thus, the 4th proportional of 3, 7 and 9 is 21.

Answer 2

Answer:

is 21

Step-by-step explanation:

3: 7 : : 9 : x

a×d :: b ×c

3x : : 9×7

3x = 63

x= 63

3

x= 21