Question

find the fourth proportional of 7,3,21​

Answer 1

✨Answer✨:

9 is the fourth proportional to 7, 3 and 21.

✨Step-by-step explanation✨:

✨Given✨:

3 terms of proportion = 7, 3 and 21

✨To Find✨:

Fourth proportional to 7, 3 and 21 = ?

✨Solution✨:

Let the fourth proportional value be 'x',

So, the proportion become = 7:3::21:x

Extreme Terms are = 7 and x

Mean Terms are = 3 and 21

We know that,

Product of Extreme Terms = Product of Mean Terms

⇒ 7 × x = 3 × 21

⇒ 7x = 63

⇒ x = $\frac{63}{7}$

⇒ x = 9

Hence, the fourth proportion is 9.

✔️Verification✔️:

Now we will verify our answer to check that is our answer exactly correct?

So, for that, we will take the help of the formula of "Product of Extreme Terms = Product of Mean Terms"

If the Product of Extreme Terms = Product of Mean Terms then our answer will be exactly correct!

⇒ 7 × 9 = 3 × 21

⇒ 63 = 63

⇒ LHS = RHS

As I told, Product of Extreme Terms and Product of Mean Terms are same. So, our answer is accurate!

Answer 2

Answer:

7 : 3 :: 21 : 9

9 is the right answer.