Question

4 times a number is 21 less than the square of that number. Find the positive solution ​

Answer 1

Explanation:

Let the number be x

by given condition,

4x = (x)² - 21

4x = x²- 21

0 = x² - 4x - 21

0 = x² - 7x + 3x - 21

0 = x ( x-7) + 3 ( x - 7)

0 = (x+3)(x-7)

hence

x + 3 =0.....

x = -3---------1

x - 7 = 0

x = 7 ------------2

we got value of x from 1 and 2.. but the question says positive value of x.

hence, x = 7 is the required value of x.